Mentioned by Allah the Almighty
Hazrat Anas bin Malik (ra) narrates that the Holy Prophet (sa) said to Ubayy (ra), “Allah has commanded me to recite to you the chapterلَمْ يَكُنِ الَّذِيْنَ كَفَرُوْا مِنْ اَهْلِ الْكِتَابِ [i.e. Surah al-Bayyinah].”
Hazrat Ubayy (ra) enquired whether God had specifically mentioned his name to which the Holy Prophet (sa) replied “Yes.” Upon hearing this, Hazrat Ubayy (ra) began to cry.
This narration is from Sahih al-Bukhari.
(Sahih al-Bukhari, Kitab Manaqib al-Ansar, Bab Manaqib Ubayy bin Kaab, Hadith 3809)
There is another narration in which Hazrat Anas bin Malik (ra) relates that the Holy Prophet (sa) said to Hazrat Ubayy (ra) bin Kaab, “Allah the Almighty has commanded me to recite the Quran to you.” Hazrat Ubayy (ra) enquired, “Did Allah mention my name to you?” to which the Holy Prophet (sa) replied, “Yes.” Hazrat Ubayy (ra) asked, “Did the Lord of this world and the Hereafter mention me?” to which the Holy Prophet (sa) replied, “Yes.” Upon this, Hazrat Ubayy’s (ra) eyes filled with tears.
(Sahih al-Bukhari, Kitab al-Tafsir, Bab Surah “Lam yakun…”, Hadith 4961)
Hazrat Musleh-e-Maud (ra) has also explained this incident in his own words. He states:
“It is narrated by Abu Hayyah Badri that Surah al-Bayyinah was revealed in its entirety, i.e. all in one go; and then Gabriel informed the Holy Prophet (sa) that Allah the Almighty had commanded him to ensure Ubayy bin Kaab (ra) memorised this chapter. The Holy Prophet (sa) said to Ubayy (ra) bin Kaab, ‘Gabriel has informed me that God Almighty has commanded that I should ensure you memorise this chapter.’ Ubayy (ra) bin Kaab said, ‘O Messenger (sa) of Allah, did God Almighty mention my name?’ The Holy Prophet (sa) replied, ‘Yes.’ Hearing this, Ubayy bin Kaab began to cry out of happiness.
(Tafsir-e-Kabir, Vol. 8, p. 342)