He divorced his wife while she was menstruating, so the Messenger of Allah ﷺ ordered him to take her back.
أخبرنا يوسف بن عيسى مروزي قال حدثنا الفضل بن موسى قال حدثنا حنظلة عن سالم
أنه طلق امرأته وهي حائض فأمره رسول الله ﷺ فراجعها
[Its isnad is sahih] Ahmad reported it: 2/61, from the hadith of Hanzala bin Abu Sufyan through him, and it is in Al-Kubra, no. 5753.