It is narrated from Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) that he said: "When we faced the enemy with the Messenger of Allah (peace and blessings be upon him), each one of us, as he advanced in the row for battle, would be far more watchful of the position of his (neighbouring) brother's knee than he was (of avoiding) an arrow when it was shot. He would say: 'Move your knee back, for I am seeking (the straightness of the row) just as you are seeking it.' Allah Almighty has said: 'As though they were a solid structure.'"
No one narrated this hadith from Burd bin Sinan (may Allah have mercy on him) except Isma'il bin Ayyash (may Allah have mercy on him), and Hisham bin Ammar (may Allah have mercy on him) is alone in narrating it.
Hadith Referenceالمعجم الأوسط / باب العين / 4563
Hadith Gradingمحدثین:إسناده ضعيف جدًّا، فيه أبو هارون العبدي متروك
Hadith Takhrij«قال الهيثمي: وفيه أبو هارون العبدي وهو متروك «مجمع الزوائد ومنبع الفوائد، ج 5، ص 326»»