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). " (PT)
English reference (PT): Vol. 3, Book 10, Hadith 2039 (PT)
Arabic reference (PT): Book 10, Hadith 2117 (PT)