[Al-Bukhari and Muslim]
He did intercourse with her thinking its his wife
According to Bahisti Zewar “A person has sexual intercourse with a woman after mistaking her for his wife. He will have to give her mahrul mithl, and this intercourse with her will not be regarded as adultery, nor will there be any sin.” [Pg 393 – point 16] – (Zam Zam publishers)
In the name of Allah, Most Gracious, Most Merciful
Assalaamu `alaykum waRahmatullahi Wabarakatoh
And Allah knows best
Wassalam
Mufti Ebrahim Desai
Darul Iftaa