Musnad Ahmad 27:233

Yahya narrated to us, from Ubaydullah, Nafi’ narrated to me, from Ibn Umar, who said: When Abdullah ibn Ubayy died, his son came to the Messenger of Allah (peace and blessings of Allah be upon him) and said: "O Messenger of Allah, give me your shirt so that I may shroud him in it, and pray over him, and ask forgiveness for him." So he gave him his shirt and said: "Inform me when he is ready." When he went to pray over him, [Umar] said: "Allah has forbidden you from praying over the hypocrites." He said: "I am between two choices: {Ask forgiveness for them or do not ask forgiveness for them} [At-Tawbah: 80]." So he prayed over him. Then Allah the Exalted revealed: {And do not pray over any one of them who has died, ever} [At-Tawbah: 84]. He said: So the prayer over them was abandoned.