Why does the gemara need to prove that you can write Torah She'Bal Peh due to Eis la'Asos from Rebbi Yochanan and Reish Lakish who read Sifrei d'Agadta? why not prove it from the fact that the Mishna was written by Rebbi Yehudah Ha'Nasi? Does it say anywhere explicitly that the writing of the Mishna was permitted due to Eis la'Asos?
Yitzchak E Gross, Inwood NY United States
1) First of all, with your question you were Mechaven to the Mahari Chagiz who asks the same two questions in his introduction to his Perush ha'Mishnayos "Eitz Chaim."* Ashrecha!
2) Everyone agrees that Rabeinu ha'Kadosh edited and closed the Mishnah. However, there is a Machlokes regarding whether Rabeinu ha'Kadosh wrote the Mishnayos or not. Some hold that even though he edited and closed the Mishnayos, they were not written down until the Gemara was committed to writing (by Ravina and Rav Ashi). According to this opinion, you have one answer to your question.
3) In the Introduction to Yad ha'Chazakah, the Shitas ha'Rambam is that after Rebbi organized, edited, and established that version as unchangeable, he then wrote down the Mishnayos. The Tosfos Rid in our Sugya states this as well. There are many indications from Shas (our Sugya being one of them) that indicate that Rebbi limited his efforts to the editing process, but did not write down the Mishnayos. Rav Nisim Ga'on writes that Ravina and Rav Ashi wrote down the Gemara and the Mishnayos. For a full dissertation on this subject, please refer to "Al Kesivas ha'Mishnah veha'Talmud" by Rav Yitzchak Isaac Stein (d. 5256/1496; he lived at the time of the Mahari Kolon), which is cited with footnotes in Igeres Rav Sherira Gaon, edited by Rav David Metzger. Rav Stein states emphatically, and brings numerous citations as proof, that not only was the Mishnah not written down in the time of Rebbi, but that even the Gemara was not written down by Ravina and Rav Ashi. He even offers another explanation to the above Rambam saying that the Rambam also concurred that Rebbi did not write the Mishnayos.
According to Rav Stein, the Mishnayos and the Gemara were written down only in the era of the Savora'im. However, Rav Metzger contends that had he seen the writings of Rav Nisim Ga'on perhaps he would have conceded to the Ga'on's opinion.
4) I had a chance to see the Mahari Chagiz inside. The facsimile of the Sefer that I saw is poor and the original print (which was very old) was also low quality, so I cannot speak definitively, but what seems to come out from the source is that although he brings "a hint" to support the Rambam from the Gemara in Shabbos 138b, in essence most of his proofs from Shas about this topic are against the Rambam, and he seems to essentially remain with "Tzarich Iyun" on the Rambam. So, in the final analysis, your question is clearly answered, that in actuality according to the overwhelming majority of opinion, the Mishnah was not written down by Rabeinu ha'Kadosh.
Shimon Brodie
? He asks that "if the Mishnah was written down by Rebbi, why was this not mentioned in the Gemara?" which is essentially your question!
I saw this brought in another Sefer, but I was not able to find it in the original due to time restrictions. I was unable to determine if (or how) he answers the question according to the Rambam.