Sayyiduna Abu Umamah (may Allah be pleased with him) said: I heard the Messenger of Allah (peace and blessings be upon him) say: "Indeed, a man stands in prayer and makes a supplication, and he is forgiven, and so are the people standing behind him."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7662