Musnad Ahmad 5:339

Ali ibn Bahr narrated to us, Abdullah ibn Ibrahim ibn Umar ibn Kaysan narrated to us, he said: My father—I heard him narrating—from Abdullah ibn Wahb, from his father, from Abu Khalifah, from Ali ibn Abi Talib, he said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "Indeed, Allah is Gentle; He loves gentleness, and He gives for gentleness what He does not give for harshness."