What is the ruling on one who had sexual intercourse with his wife after their marriage was annulled, while he was unaware of the annulment?

The annulment of marriage (faskh (definition) an-nikah (definition)) can occur for several reasons, including: lack of compatibility, apostasy of one of the spouses, the husband embracing Islam and the non-scriptural wife refusing Islam, mutual imprecation (li'an), the husband's inability to provide maintenance, the presence of a defect preventing enjoyment, or khul' (divorce at the wife's instance) according to those who consider it an annulment. It usually requires a judge's ruling.

If a man has intercourse with his wife after the annulment, unaware of it and believing her to still be his wife, this is an intercourse of شبهة (shubhah - شبهة, "doubt/error") for which there is no sin. The child is attributed to him and inherits from him by consensus of the Muslims. Even if the wife knew of the annulment, she is sinful for allowing it, but the child is attributed to the father due to his ignorance.

After the annulment, the wife cannot return to her husband except through a new contract that fulfills all conditions. Neither intercourse nor verbal declaration can reinstate her.