It is narrated from Sayyiduna Irbad bin Sariyah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) used to invoke blessings upon the first row three times, and upon the one next to it (the second row) once.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5194