Musannaf Ibn Abi Shayba 34:291

Khalid ibn Makhlad narrated to us, he said: Musa narrated to me, he said: Muhammad ibn Amr ibn Ali informed me, from Ali ibn Abi Talib, he said: The first to be buried in al-Baqi was Uthman ibn Maz'un, then Ibrahim, the son of the Messenger of Allah, may Allah bless him and grant him peace, followed him.