Majma al-Zawaid — Hadith 1891

Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) states: During a journey the Prophet (peace and blessings be upon him) heard a mu'adhdhin saying "Allahu akbar, Allahu akbar (Allah is the Greatest, Allah is the Greatest)," and he said, "He is upon the fitrah (natural disposition)." When he recited "Ashhadu an la ilaha illallah (I bear witness that there is no god but Allah)," the Prophet (peace and blessings be upon him) said, "He has borne witness to the truth." When he recited "Ashhadu anna Muhammadan rasulullah (I bear witness that Muhammad is the Messenger of Allah)," the Prophet (peace and blessings be upon him) said, "He has come out of Hell. Look for him; you will find that he is either a shepherd who is far from his family or someone who hunts with dogs." When the people looked for him, they found that he was a shepherd for whom the time of prayer had come, so he had given the adhan for the prayer.
Imam Ahmad and Imam al-Tabarani in al-Mu'jam al-Saghir recorded this narration. Its chain contains a narrator, al-Hakam bin Abd al-Malik al-Qurashi, who is da'if (weak).