Yevamos 4:9-10

Yevamos 4:9

What if a woman is waiting to perform yibum or chalitzah with her deceased husband’s brother and, in the interim, his brother becomes betrothed to her sister? The Sages say in the name of Rabbi Yehuda ben Beseira that the betrothed brother is told to wait for his older brother to act. If the brother performs yibum or chalitzah, the betrothed brother may then proceed. If the widow dies, the betrothed brother may proceed. If the brother who is waiting to act dies, the betrothed brother must divorce the sister and perform chalitzah with the widow.

Yevamos 4:10

The widow must wait three months to perform yibum or chalitzah (to ensure that she’s not pregnant). No women who were widowed or divorced may be betrothed or married until they have waited three months, whether they were widowed or divorced from a status of betrothal or marriage. Rabbi Yehuda says that women who were married may become betrothed and those who were betrothed may get married, except for women from Judea whose fiancés are suspected of consummating the relationship before the actual marriage. Rabbi Yosi says that all women may be betrothed except for widows because they are in mourning.