Sa’ad from Muhammad ibn al-Husayn from al-Hakam ibn Miskin from Ishaq ibn Ammar, who said: I said to Abu Abdillah عليه السلام, peace be upon him: “I enter the mosque and the imam (of prayer) has already bowed, so I bow with his bowing while I am alone (away from the congregation), and I prostrate. When I raise my head, what should I do?” Imam عليه السلام said: “Stand and go to them (to join the congregation); if they are standing, then stand with them, and if they are sitting, then sit with them.”