Musnad Ahmad 482:100

Sufyan narrated to us, from Ibn Jurayj, who said: I heard Abu Sa’d narrating to ‘Ata’, he said: Abu Ayyub traveled to ‘Uqbah ibn ‘Amir. He came to Maslamah ibn Mukhallad, and he came out to him, and he (Abu Ayyub) said: "Direct me." So he came to ‘Uqbah and said: "Narrate to us what you heard from the Messenger of Allah (ﷺ), for there remains no one who heard it (besides you)." He said: I heard the Messenger of Allah (ﷺ) say: "Whoever conceals a believer in this world, Allah will conceal him on the Day of Resurrection." Then he went to his mount, mounted it, and returned.