It is narrated from Sayyiduna Salman al-Farisi (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "When a man in a land of shade gives the adhan at the time of prayer, gives the iqamah for the prayer and prays, angels form a row behind him whose ends cannot be seen; they bow with his bowing, prostrate with his prostration and say Amin to his supplication."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1908