Musannaf Ibn Abi Shayba 36:570

Al-Fadl ibn Dukayn narrated to us, from al-Walid ibn Jumay', from Abu al-Tufayl, who said: There was between Hudhayfah and a man among them—from the people of al-'Aqabah—some of what occurs between people. He said, "I adjure you by Allah, how many were the companions of al-'Aqabah?" The people said, "Inform him, for he has asked you." Abu Musa al-Ash'ari said, "We used to be told that they were fourteen." Hudhayfah said, "And if I were among them, then they were fifteen. I bear witness by Allah that twelve of them are the party of Allah and His Messenger in the life of this world and on the day when the witnesses arise." And he excused three, who said, "We did not hear the caller of the Messenger of Allah (may Allah bless him and grant him peace), nor did we know what the people intended."