Bulugh al-Maram #1270

Narrated : A man had vowed to make his wife like his mother (i.e. forbidden for him). Then he had intercourse with her, so he went to the Prophet (ﷺ) and said, "I had intercourse with her before making the atonement." He replied, "Do not go near her till you do what Allah has commanded you to do." Reported by al-Arba'a. at-Tirmidhi graded it Sahih (authentic) but an-Nasa'i held that the stronger view is that it is Mursal (missing link after the Tabi'i)].