Gemara

105a (Mishnah): If he knows that he specified which type of Minchah he will bring, but does not remember which, he must bring all five.

106b (Mishnah): If one says 'I specified how much I will bring, but I do not remember how much', he must bring an amount that he is sure that he did not vow more than this.

Chulin 134a (Mishnah): A convert must give Matanos (the foreleg, jaw and stomach) to a Kohen from his cow only if it was slaughtered before he converted. If we are unsure, he is exempt. The Kohen cannot take from him without proof.

Contradiction (Mishnah): If grain was found in an ant-hole in a place that was already harvested, what rests on top must be left for the poor;

R. Meir says, even what is inside must be left for the poor, because Safek Leket is Leket.

(Reish Lakish): "Ani va'Rash Hatzdiku" cannot mean to vindicate the poor, for it says "v'Dal Lo Sehedar b'Rivo"! Rather, give to him what you were entitled to keep (if not for this verse).

Answer (Rava): The Chazakah is that Leket must be left from the grain, but (until the Nochri converts) the cow is exempt from Matanos Kehunah.

Question (Abaye - Mishnah): If a Nochri converted with a dough, he must separate Chalah only if it was kneaded after he converted. If we are unsure, he must take.

Answer (Rava): One may not eat without taking Chalah, so Safek Isur l'Chumra. Matanos are a monetary privilege of the Kohen, and Safek Mamon l'Kula.

Bava Basra 148b - Question: If a Shechiv Mera made all his property Hekdesh, and recovered, what is the law?

Regarding Hekdesh, does one decide absolutely to give it (even if he will recover)? Or, one never abandons himself (to be left without anything if he recovers)?

Question: If gave all his property to the poor, what is the law?

Do we say that regarding the Mitzvah of Tzedakah, surely he decided absolutely to give it? Or, do we say that one never abandons himself?

These questions are unsettled.

Rishonim

Rambam (Hilchos Zechiyah 9:19): If a Shechiv Mera made all his property Hekdesh, or gave all his property to the poor and recovered, he may retract.

Rosh (Nedarim 1:3 and Ramban on Rif 1b): The Gemara did not resolve whether Yesh Yad l'Tzedakah, therefore we are stringent.

Rebuttal (Ran 7a DH ul'Inyan): Also the Rashba considers this Safek Isur l'Chumra. Chulin 134a says that Safek Mamon Aniyim is Safek Mamon, and we are lenient (for the giver)! Safek Leket is Leket because due to Chazakah (he was obligated). If it were Safek Isur, there would be no need to say this! Yoma (8b) understood that we are lenient about Ma'aser Oni of Demai (i.e. Safek) because ha'Motzi me'Chavero Alav ha'Re'ayah, but asked why we are lenient about Ma'aser Sheni. This is because Ma'aser Sheni is Safek Isur, and Ma'aser Oni is Safek Mamon!

Rosh (Bava Basra 9:23): The Gemara did not resolve about a Shechiv Mera who was Makdish his property to Hekdesh or Aniyim. Since it was not resolved, we are unsure whether Umdena (estimation of his intent) applies. It seems that we annul the Hekdesh or Tzedakah only when there is a clear Umdena.

Teshuvas ha'Rashba (1:656): A case occurred in which Reuven handed over a box to two men, and said that he is Makdish (for Aniyim) things inside, and also houses, lest he die on his journey. He explained that his son does not treat him properly, and he wants to atone for himself (through Tzedakah). He died. His son claimed that his father said so only due to anger, and he says that he has witnesses in another city that he retracted.

Rashba: Even if he was Makdish due to anger, and retracted, the Aniyim acquired, unless he permitted his vow. He cannot permit what is in the box, for we are the Yad (power of acquisition) of Aniyim. One cannot retract once the recipient received it. However, it is not clear whether he stipulated about dying before reaching his destination, or before returning home. Since he attributed his Hekdesh to his attitude towards his son, it seems that he wanted to be Makdish in any case. If we are unsure whether he intended to return, we are lenient for the heirs. They are Muchzakim. The Aniyim must prove that the Tanai was fulfilled, just like regarding Safek Matanos Kehunah. Safek Isur l'Chumra does not apply to Hekdesh Aniyim. Even regarding Hekdesh Bedek ha'Bayis, we follow Chezkas Mamon if it is a Safek whether Hekdesh took effect. We never resolved whether a Shechiv Mera can retract from Hekdesh or Hekdesh to Aniyim (Bava Basra 148b). We are lenient about the Safek. The Rambam says so. Perhaps even the opposing opinion is stringent only if Hekdesh took effect and it is a Safek if he retracted, but he agrees that we do not take from a Muchzak if perhaps the Hekdesh never took effect.

Mordechai (Bava Basra 659, cited in Beis Yosef YD 259 DH Kosav Od): Toras Kohanim and the Yerushalmi expound that Safek Leket, Shichchah and Pe'ah must be left for Aniyim. We may learn to Safek Tzedakah.

The questioner in Rivash 160: The Rambam says that Hekdesh cannot take from heirs because they are Muchzakim, but if Aniyim made a Chazakah in their portion, they keep it.

Rivash: Even though there is an Isur of Safek Hekdesh, and words to Hekdesh are like handing over to a person, the Rambam says that Hekdesh cannot take from the heirs. All the more so Aniyim cannot take from the heirs. Heirs have a Chazakah like their father did. Shmuel had a Safek, that perhaps one who gave a document intended that it work only after death. Due to this, he annuls the gift, and the heirs keep the property. If the document gave only part to Hekdesh, and the rest to the heirs, the heirs definitely receive, and Hekdesh is Safek, and Safek cannot take from Vadai.

Poskim

Shulchan Aruch (CM 250:3): If a Shechiv Mera made all his property Hekdesh, or gave it all to the poor and recovered, it is all Batel, like the law of his gift.

Beis Yosef (DH u'Mah she'Chasav v'Im): The Rambam holds like this. The Magid Mishneh explains that since the Gemara did not resolve this, one cannot take from him without a proof. Also the Tur says so in the name of the Ramah. I do not understand the Rosh. There is a clear Umdena that one does not leave everything to others, and he will need to beg! Because it is a Mitzvah, we have a Safek. Therefore, we do not take, like the Rambam and Ramah. The questioner in the Rivash said that the Aniyim already made a Chazakah in their portion. This is not a Chazakah. It is mere seizure of what is not theirs. The heir has a clear Chazakah (he inherits automatically). Hekdesh seeks to take due to the command (of the deceased), which is a Safek. A Safek cannot take from a Vadai. If both sides acquire only through the command, perhaps Tefisah (seizing) Metaltelim would help Hekdesh. Tefisah does not help for land, and some say that it does not help for Metaltelim if witnesses saw the party seize. The Ramban holds that even without witnesses, Tefisah helps only if the Safek is due to the contradictory claims, but not if it is due to the law itself, e.g. the Gemara did not resolve it. Since the one holding the money should keep it, even if one seized without witnesses, we return it. This is reasonable, even though the Rambam (Hilchos Zechiyah 4:3) holds that sometimes when the Gemara never decided, if one seized, he keeps it.

Rebuttal (Prishah 4 DH v'Ein): The Rosh and Tur hold that saying to give to Aniyim is like handing over (to them). It is as if they received and totally acquired at the time. We do not say that Hekdesh (the Aniyim) seeks to take from the heirs. Hekdesh is somewhat Muchzak! However, the giver can retract if he recovers. There is an Umdena that one does not abandon himself, but it is not so strong regarding Hekdesh and Aniyim (for it is a Mitzvah to give to them). The Tur does not cite the Rosh to say 'we do not Mevatel his words due to Safek', rather, his actions. This is because his words are considered as if he gave to them, and now he wants to retract. This is not because words of a Shechiv Mera are as if they were written and given over. That applies only if he dies, and then it is as if they were written and given over retroactively. Hekdesh or a vow to Aniyim is immediately considered as if it was given. The Rosh proved this from the Halachah that the giver can retract only if we know that he had no other property. This is if he gave with a Kinyan, for we do not annul an act (Kinyan) due to an Umdena, since perhaps he had other property.

Rema: Even if the Aniyim seized, we take from them. This is unlike the opposing opinion.

Taz (3): It is not clear why here, the Rema rules that we do not take from Aniyim due to a Safek Isur. He wrote similarly in YD 258:5, but in 258:2 he rules like the Rosh.

Gra (11): This is like the Rema rules in YD 315:1, that if the Kohen seizes (a Safek Bechor), we take it from him.

Gra (12): The opposing opinion holds that even without Tefisah, he cannot retract.

Shulchan Aruch (YD 258:3): If one says 'I specified how much I will bring, but I do not remember how much', he must bring an amount that he is sure that he did not vow more than this.

Shulchan Aruch (259:5): If one has money and he is unsure whether it is of Tzedakah, he must give it to Tzedakah.

Chasam Sofer (YD Sof 240): We are stringent about Safek Tzedakah, so it is like Safek Hekdesh. If one pledged to Hekdesh and does not remember how much, he brings an amount that he knows that he did not vow more than this.

Pischei Teshuvah (10): The Chasam Sofer brings other Rishonim who hold like the Rosh, Ramban and Rashba, that Safek Tzedakah is like Safek Isur. Only the Ran and Nimukei Yosef disagree; we do not follow them. The Oni is Muchzak. However, if the giver has a Vadai claim, e.g. a Shechiv Mera who recovered, he wins. This is even if one has a claim against him, e.g. he pledged to a particular Tzedakah. This is unlike the Rosh (Bava Basra 9:23).

Rema: However, if one was Makdish something with a Safek expression and he died, the heirs are Muchzakim. Hekdesh cannot take from them without a proof.

Question (Taz 3): Above (258:2), the Rema (agreed with the Shulchan Aruch, who) ruled that Yesh Yad l'Tzedakah, i.e. because it is Safek Isur l'Chumra!

Answer #1 (Shach 14): The Rema holds that the Mordechai and the Rashba do not argue. (He rules like both of them.) Regarding heirs, this is not considered Safek Isur. However, the Rashba equates heirs and the Makdish. He brought proofs from Matanos and a Shechiv Mera who retracted! Also the Terumas ha'Deshen (Sof 2:73) and Rivash (160) equate them.

Answer #2 (Taz): The Rema is lenient if it was feasible for the Safek to be resolved. A Makdish is believed to explain what he meant. There is no way to resolve whether Yesh Yad l'Tzedakah, so the Rema is stringent.

Shach (14): Safek 'Hekdesh' for Aniyim or the Beis ha'Keneses is not considered Safek Isur about which we must be stringent. Rather, it is a monetary Safek, so ha'Motzi me'Chavero Alav ha'Re'ayah. Even though we are stringent about Safek Leket, Shichchah and Pe'ah (Chulin 134a), this is because the Chazakah was that the Matanos must be left. We always follow the Chazakah.