Is it permissible to eat from a banquet prepared by a man who vowed to slaughter a banquet if a woman aborted her pregnancy by him, given that she committed adultery with him and aborted the pregnancy?

It is not permissible to abort the fetus, even before the ensoulment. The two who committed adultery must repent. Scholars have differed regarding eating from vowed food (food offered as part of a vow), and the more cautious opinion is not to eat from it. A vow contingent on abortion is not valid according to some scholars, because it is a vow contingent on committing a sin. This is the view preferred by Ibn Hajar Al-Haytami, and it is permissible to eat from such a vow.