Shalom Rabbi
Hope all is well with you. If a man sleeps with his brother's childless widow(Yevamah) before marrying and has a son,
1)Does he fulfill the Misvah of Yibbum? Meaning is marriage an integral part of the Misvah or is it enough just to have a child?
2) And if he has a child with his Yevamah before marrying her, Is there still a Misvah to marry her?
3) Is the Din different before Matan Torah? Did Yehudah fulfill the Misvah with the birth of Tamar's twins?
4) Was there still a Misvah of Yibbum on Yehudah or Shelah after the birth of the twins?
Thank you and Shabbat Shalom
Aaron Shemtob
The Mitzvah of Yibum is a one-time Bi'ah with the widow. On the Torah (d'Oraisa) level, no marriage is needed before (Rambam, Hilchos Yibum 1:1). Only mid'Rabanan is marriage required first, but if not done, the Mitzvah was still done and finished (Rambam, Hilchos Yibum 2:2).
Also, even if no child is born, the Mitzvah was done and completed with the act of Bi'ah.
The Torah's Mitzvah of Yibum did not exist before Matan Torah like all Mitzvos. By Yehudah and Tamar, the Ramban (Bereishis 38:8) mentions the "secret of the widow remarrying to the husband's family" and whether it existed even before Yehudah.
There is no Mitzvah to do once Yehudah took Tamar.
All the best,
Reuven Weiner
Thank you rabbi
There is an opinion in Sotah that says Kivan she'Yad'ah Shuv Lo Pasak Memenah-
Once Yehudah saw that she was leshem shamayim
he continued relations with her
1) Are we to assume that it means he Married her?
2) Even if he married her, if he already fulfilled the Mitzvah then it was Assur because of Ervat Kalato?
Dear Aaron,
That is correct -- continuing with her means he married her.
By every brother-in-law there is the Isur of Eshes Ach, but by Yibum the Torah permits it, and even after the Mitzvah has been done, the Torah's Heter remains. Here also, it continues to be permitted.
All the best,
Reuven Weiner