Musannaf Ibn Abi Shayba 21:521

Ghundar narrated to us, from Shu'bah, from Mughirah, who said: Al-Hakam said to Ibrahim: "I saw Abu Bakr bin Abd al-Rahman bin al-Harith standing on Al-Safa for the duration it takes a man to recite one hundred and twenty verses." He said: "He is indeed a jurist."