Sayyiduna Abdullah bin Amr (may Allah be pleased with him) says: The mu'adhdhin calls the adhan, and then some people also pray who are not (in reality) believers.
Al-Tabarani recorded it in al-Mu'jam al-Kabir, and its chain contains a man who has not been named.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الإيمان / 440