Who was the Companion whom Allah commanded His Messenger (peace and blessings be upon him) to recite Surat Al-Bayyinah to?

The Companion in question is Ubayy ibn Ka'b, may Allah be pleased with him. This is based on what Anas ibn Malik, may Allah be pleased with him, narrated, that the Prophet, peace and blessings be upon him, said to Ubayy: "Indeed, Allah has commanded me to recite to you: 'Those who disbelieved among the People of the Scripture...' (Surah Al-Bayyinah)." Ubayy asked: "And did He mention me by name?" The Prophet replied: "Yes." So Ubayy wept. (Agreed upon).