Muwatta Imam Malik Book of Marriage, Hadith 56

Yahya related to me from Malik from Yahya ibn Said that Said ibn al-Musayyab said, "There are three things in which there is no jest:
marriage, divorce, and setting free."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، أَنَّهُ قَالَ ثَلاَثٌ لَيْسَ فِيهِنَّ لَعِبٌ النِّكَاحُ وَالطَّلاَقُ وَالْعِتْقُ .