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