What is the ruling on a man marrying a woman whom he had intercourse with twenty days before the end of her waiting period, and what is the ruling concerning their child? Is it permissible for the man to marry her again if they are separated?

Marriage during the iddah (waiting period) is invalid by consensus. If it occurred out of ignorance, it is a nikah shubhah (marriage by misconception), carrying no sin, and the child is attributed to the man if born six months after the consummation. However, if it occurred with knowledge of its prohibition, it is zina (fornication), and the children are not attributed to the father but are ascribed to the mother. The preponderant opinion is the permissibility of contracting marriage with her after their separation and the expiry of her first waiting period.