The freed slave of Usama bin Zaid said,

"Al-Hajjaj bin Aiman bin Um Aiman and Aiman Ibn Um Aiman was Usama's brother from the maternal side, and he was one of the Ansar. He was seen by Ibn 'Umar not performing his bowing and prostrations in a perfect manner. So Ibn 'Umar told him to repeat his prayer.

Sahih al-Bukhari Book 62, Hadith 83