٥ـ عَلِيُّ بْنُ إِبْرَاهِيمَ عَنْ أَبِيهِ عَنْ عَبْدِ الله بْنِ الْمُغِيرَةِ قَالَ فِي كِتَابِ حَرِيزٍ أَنَّهُ قَالَ إِنِّي نَسِيتُ أَنِّي فِي صَلاَةٍ فَرِيضَةٍ حَتَّى رَكَعْتُ وَأَنَا أَنْوِيهَا تَطَوُّعاً قَالَ فَقَالَ هِيَ الَّتِي قُمْتَ فِيهَا إِنْ كُنْتَ قُمْتَ وَأَنْتَ تَنْوِي فَرِيضَةً ثُمَّ دَخَلَكَ الشَّكُّ فَأَنْتَ فِي الْفَرِيضَةِ وَإِنْ كُنْتَ دَخَلْتَ فِي نَافِلَةٍ فَنَوَيْتَهَا فَرِيضَةً فَأَنْتَ فِي النَّافِلَةِ وَإِنْ كُنْتَ دَخَلْتَ فِي فَرِيضَةٍ ثُمَّ ذَكَرْتَ نَافِلَةً كَانَتْ عَلَيْكَ فَامْضِ فِي الْفَرِيضَةِ. 
5. Ali ibn Ibrahim has narrated from his father from ‘Abd Allah ibn al-Mughirah who has said the following: “It is in the book of Hariz who has said that once I forgot about my being in obligatory Salah (prayer) until Ruku‘ (bowing down on one’s knees). Can I make my intention for it to be an optional Salah (prayer)? He (the Imam) , said, ‘It is what you had stood up for. If you stood up to perform an obligatory Salah (prayer) then doubts entered, you are still in obligatory Salah (prayer). If you stood up for optional Salah (prayer) then made your intention for obligatory Salah (prayer), you were still in optional Salah (prayer). If you stood up for obligatory then you remembered optional Salah (prayer) which was due, you were to complete it as obligatory.’” 