Sayyiduna Abu al-Darda' (may Allah be pleased with him) says: In the Days of Ignorance (Jahiliyyah) a man would divorce, then take his wife back and say: "I was only joking." Likewise he would free a slave, then go back on it and say: "I was only joking." Then Allah Almighty revealed this verse: "Do not take the verses of Allah in jest." So the Prophet (peace and blessings be upon him) said: "Whoever divorces, or declares something forbidden, or marries, or gives someone in marriage, and then says: 'I was only joking,' it will be counted as serious."
Imam al-Tabarani recorded it; its chain contains a narrator, Amr bin Ubayd, and he is one of the enemies of Allah. I say: A hadith of this kind will come later in the chapter on "Divorce".
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب النكاح / 7529