From him, from Hamdawayh, from Muhammad ibn Al-Husayn, from Al-Hasan ibn Mahbub, from Abd Al-‘Aziz, from Abdullah ibn Abi Ya‘fur, from Abu Abdillah عليه السلام, peace be upon him, who said: I asked Imam عليه السلام about a man who stands for an obligatory prayer and prays one rak‘ah while intending it as a recommended (nafilah) prayer. Imam عليه السلام said: "It is according to what you stood up for and intended." And Imam عليه السلام said: "If you stand intending an obligatory prayer and doubt enters you afterward, then you are in the obligatory prayer based on the intention you stood with. But if you entered it intending a recommended prayer, and then afterward changed the intention to an obligatory prayer, then you are still in the recommended prayer. Only that part of the prayer is counted for the servant which he began with the original intention."