Maliks Muwatta Book 29, Hadith Number 81.

Section : General Section on Divorce.

Yahya related to me from Malik from Thawr ibn Zayd ad-Dili that Allah, the Blessed, the Exalted, sent down about a man who divorced his wife and then returned to her while he had no need of her and did not mean to keep her so as to make the idda period long for her by that in order to do her harm, “Do not retain them by force, to transgress. Whoever does that has wronged himself.” (Sura 2 ayat 231). Allah warns them by that ayat.