Chapter on Rulings on Forgetfulness (Sahw) in Prayer and What Requires Repeating of Prayer

Al-‘Ayyashi, from Ja‘far bin Ahmad, said Ali bin al-Hasan and Ali bin Muhammad narrated to me, from Muhammad bin ‘Isa, from Yunus, from Mu‘awiyah, who said: I asked Abu Abdillah عليه السلام about a man who stood to pray an obligatory prayer (‘al-maktubah’), then became confused and thought it was a recommended prayer (‘nafilah’), or he stood to pray a ‘nafilah’ and thought it was an obligatory prayer. Imam عليه السلام said: “It is according to what he began the prayer with.”