Reference: Majmoo’ Fataawa wa Rasaa.il Muhammad ibn Saalih al-‘Uthaymeen – Volume 13, Fatwa No.394
Question: What is the ruling of completing and straightening the rows for the funeral prayer?
Response: The rows in the funeral prayer are like other rows, except the scholars have recommended the rows should not have less than three [men], even if the first rows are incomplete.