Musannaf Ibn Abi Shaybah 3570 — Straightening the row

Malik bin Abi Amir said: Sayyiduna Uthman (may Allah be pleased with him) used to say: "Stand level and keep the shoulders in line, for straightening the rows is part of the completeness of the prayer." Sayyiduna Uthman would not say the opening takbir until the men whom he had appointed to straighten the rows came and informed him.