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.