Musnad Abu Ya'la al-Mawsili 3:230

Ishaq ibn Abi Isra'il narrated to us, Hisham ibn Yusuf narrated to us, Ibrahim ibn 'Umar narrated to me, 'Abdullah ibn Wahb ibn Munabbih narrated to me, from his father, from Abu Khalifah, from 'Ali ibn Abi Talib, from the Prophet (may Allah bless him and grant him peace), who said: "Indeed, Allah is Gentle; He loves gentleness and He gives for it what He does not give for harshness."