The prayer was called, and the Messenger of Allah ﷺ turned his face toward us and said, "Straighten your rows and stand close together, for I see you from behind my back."
أقيمت الصلاة، فأقبل علينا رسول الله ﷺ بوجهه فقال: أقيموا صفوفكم وتراصوا، فإني أراكم من وراء ظهري.
Bukhari narrated it in the Book of Adhan (719), and Muslim in the Book of Prayer (434), both through different routes from Anas bin Malik, and the wording given is Bukhari's. Muslim's wording is, "Complete the rows, for indeed I see you from behind my back." In another version with Bukhari (725), "Straighten your rows, for indeed I see you from behind my back," and each of us would press his shoulder against his companion's shoulder, and his foot against his foot. And in Abdul-Razzaq's version (2/44), "Maintain these rows, for indeed I see you from behind me."He said in Fath al-Bari (2/211), his saying "from Anas" was narrated by Saeed bin Mansur, from Hushaym, who explicitly stated in it that Anas reported it to Humayd, and it contains the addition at its end, namely his saying, "and each of us would... etc.," and he made clear that this was Anas's own statement. Ismaili narrated it through Mamar's route, from Humayd, with the wording, Anas said, "I indeed saw one of us... etc." This explicit statement establishes that the action mentioned took place during the time of the Prophet ﷺ, and with this the argument is completed for clarifying what is meant by straightening and aligning the row. Mamar added in his version, "and if I did that to one of them today, he would bolt as if he were a stubborn mule." End of quote.His saying "tarassu" with the doubling of the letter sad without a dot, meaning press closely together without any gap, and it is possible that it is a reinforcement of his saying "aqimu." What is meant by his saying "aqimu" is "make even," it is said, "the stick was made qaim," when it is straightened and made even. As for his saying, "Indeed I see you from behind my back," the majority took it literally, because of the honor it contains for the Prophet ﷺ.