Sayyiduna Irbad bin Sariyah (may Allah be pleased with him) narrates from the Messenger of Allah (peace and blessings be upon him) that he (peace and blessings be upon him) "sought forgiveness for the first row three times, and for the second row once."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5195