Ahmad from al-Husayn from al-Nadr from Hisham ibn Salim from Sulayman ibn Khalid from Abu Abdillah عليه السلام, peace be upon him, who said: I asked Imam al-Sadiq عليه السلام about a man who enters the mosque and begins the prayer. While he is standing and praying, the muezzin gives the call to prayer and establishes the congregational prayer. Imam عليه السلام said: “Then let him complete two rak‘ahs and begin the prayer anew with the imam (of prayer), and let the two rak‘ahs be counted as voluntary (nafl) prayer.”