Sahih Bukhari Volume 005, Book 057, Hadith Number 081.

Narated By Usama bin Zaid : That the Prophet used to take him (i.e. Usama) and Al-Hassan (in his lap) and say: "O Allah! Love them, as I love them." 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. Harmala, the freed slave of Usama bin Zaid said that while he was in the company of 'Abdullah bin 'Umar, Al-Hajjaj bin Aiman came in and (while praying) he did not perform his bowing and prostrations properly. So Ibn 'Umar told him to repeat his prayer. When he went away, Ibn 'Umar asked me, "Who is he?" I said, "Al-Hajjaj bin Um Aiman." Ibn 'Umar said, "If Allah's Apostle saw him, he would have loved him." Then Ibn 'Umar mentioned the love of the Prophet for the children of Um Aimn. Sulaiman said that Um Aiman was one of the nurses of the Prophet.