From Sahih Muslim (Hadith 977):
Hammam b. Munabbih reported:This is what was transmitted to us by Abu Huraira from the Messenger of Allah (ﷺ) and, while making a mention of a few ahadith, said: (The Messengerof Allah directed us thus): Establish rows in prayer, for the making of a row (straight) is one of the merits of prayer
Reference: Muslim 977