Musnad Ahmad 18:1

Al-Hakam ibn Nafi' narrated to us, Isma'il ibn 'Ayyash narrated to us, from Salim ibn 'Abdullah, from 'Abdullah ibn Muhammad ibn 'Aqil, who said: 'Aqil ibn Abi Talib got married, so he came out to us. We said to him, "With concord and sons." He said, "Desist. Do not say that, for the Prophet, peace and blessings of Allah be upon him, has forbidden us from that, and he said: 'Say: May Allah bless you, and may He bless you in her.'"