Chapter on the Detailed Explanation of Prayer, Including the Obligatory and Recommended, and What is Permissible and Not Permissible.

And from him, from Ali ibn Ibrahim, from his father, from Ibn Abi ‘Umayr, from Ibn Udhaynah, from Zurarah, from Abu Ja’far عليه السلام: He عليه السلام was asked about a man who prayed without ritual purification (‘tahur’), or forgot a prayer and did not perform it, or slept through it. Imam عليه السلام said: "He should make it up whenever he remembers it, at whatever hour he remembers, by night or by day. But if the time of another prayer enters and he has not yet completed the missed one, then let him continue, as long as he does not fear that the time for the present prayer will expire. If he fears that, then this current prayer takes precedence, so let him pray it. Then, once he has prayed it, he should make up the missed prayer afterwards. And he must not perform any supererogatory (‘nafl’) rak’ah until he has made up all of the obligatory (‘faridah’) prayers."