Musnad Ahmad 256:1

Abu Sa’id, the freed slave of Banu Hashim, narrated to us, saying: Hammad ibn Salamah narrated to us, from ‘Ali ibn Zayd, from ‘Ammar ibn Abi ‘Ammar, from Abu Hubbah al-Badri, who said: When "Lam Yakun" (Surah al-Bayyinah) was revealed, Jibril (peace be upon him) said: "O Muhammad, your Lord commands you to recite this Surah to Ubayy ibn Ka’b." The Prophet (peace and blessings of Allah be upon him) said: "O Ubayy, my Lord, the Mighty and Majestic, has commanded me to recite this Surah to you." He wept and said: "Was I mentioned there?" He (the Prophet) said: "Yes."