Al-Kāfi
Hadith 10764ـ مُحَمَّدُ بْنُ يَحْيَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنِ الْحُسَيْنِ بْنِ سَعِيدٍ عَنْ عُثْمَانَ بْنِ عِيسَى عَنْ إِسْحَاقَ بْنِ عَمَّارٍ قَالَ قُلْتُ أُصَلِّي فِي وَقْتِ فَرِيضَةٍ نَافِلَةً قَالَ نَعَمْ فِي أَوَّلِ الْوَقْتِ إِذَا كُنْتَ مَعَ إِمَامٍ تَقْتَدِي بِهِ فَإِذَا كُنْتَ وَحْدَكَ فَابْدَأْ بِالْمَكْتُوبَةِ.
4. Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from al-Husayn ibn Sa‘id from ‘Uthman ibn ‘Isa from Ishaq ibn ‘Ammar who has said the following: “I once asked him (the Imam) (a.s.), ‘Can I perform optional Salah (prayer) in the time for obligatory one?’ He (the Imam) replied, ‘Yes, you can do so in the beginning of time if you are with the Imam who leads you in Salah (prayer). If you are alone, then perform the obligatory first.’”