Sayyiduna Ruwayfi’ bin Thabit Al-Ansari (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: Whoever believes in Allah and the Last Day, it is not permissible for him to let his water (semen) flow into another’s child, nor is it permissible for him not to let his water flow into another’s child (i.e., he should not have intercourse with a pregnant woman who is carrying another man’s child).