Sahih Muslim Book 4, Hadith Number 1747.

Chapter : Excellence of the one who is proficient in the Qur’an and one who falters in it.

Anas reported Allah’s Messenger (may peace be upon him) as saying to Ubayy b. Ka’b: Allah has commanded me to recite the Qur’an to you. He said: Did Allah mention me to you by name? He (the Holy Prophet) said: Allah made a mention of your name to me. (On hearing this) Ubayy b. Ka’b wept.