It is narrated from Sayyiduna Fadalah bin Ubayd al-Ansari (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "There are three things in which jesting is not permissible: divorce, marriage, and freeing a slave."
Hadith Referenceالمعجم الكبير للطبراني / باب الفاء / 15871