I know I have heard of this prohibition based on the Muslims false origin of the Jews, maybe it was only a fatwa. The Palestinian Authority Imam has proclaimed their false origin story, but that doesn’t stop the terrorists in the field.
From Ali Sina's book "Understanding Muhammad".
p. 39 Rape
Muhammad allowed his men to rape the women captured in raids. However Muslims faced a dilemma. They wanted to have sex with their female captives, but also wanted to return them for ransom and therefore did not want to make them pregnant. Some of these women were already married whose husbands had escaped when taken by surprise and were still alive. The raiders considered the possibility of "coitus interruptus" (withdrawing from intercourse before ejaculation). Unsure of the best course of action, they sought the counsel of their Prophet. Buhkari reports:
Abu Saeed said "We went out with Allah's Apostle for the Ghazwa of Banu Al-Mustaliq and we received captives from among the Arab captives and we desired women and celibacy became hard on us and we loved to do coitus interruptus. So when we intended to do coitus interruptus, we said "How can we do coitus interruptus before asking Allah's Apostle who is present among us?" We asked (him) about it and he said "It is better for you not to do so, for if any soul (till the Day of Resurrection) is predestined to exists, it will exist.
Bukhari, Volume 5, Book 59, Number 459.
Muhammed did not forbid raping the captive women. Instead he made an asinine claim that when Allah intends to create someone, nothing can prevent it. He told his men that coitus interruptus is ill-advised because it would be an attempt to thwart the will of Allah. He did not say a word against the rape of the captives, and by discouraging coitus interruptus, he supported forced insemination.
He made even his god legitimize with women captured in wars, the so-called "right hand possessions," even if they were married before their capture.