It was narrated from Abu Hurairah that:
the Messenger of Allah (ﷺ) said: "There are three matters in which seriousness is serious and joking is serious: marriage, divorce and taking back (one's wife). " (ES)
English reference (ES): Vol. 3, Book 10, Hadith 2039 (ES)
Arabic reference (ES): Book 10, Hadith 2117 (ES)