Al-Kāfi - The Book of Prayer

Chapter: Where to Apply Rules about Salah (Prayer) on a Journey 4ـ عَلِيُّ بْنُ إِبْرَاهِي٠َ عَنْ أَبِيهِ عَنْ حَ٠َّادٍ عَنْ حَرِيزٍ عَنْ ٠ٍ قَالَ سَأَلْتُ أَبَا عَبْدِ الله (عَلَيْهِ الْسَّلا٠) عَنْ رَجُلٍ يَدْخُلُ ٠ِنْ سَفَرِهِ وَقَدْ دَخَلَ وَقْتُ الصَّلاَةِ قَالَ يُصَلِّي رَكْعَتَيْنِ فَإِذَا خَرَجَ إِلَى سَفَرٍ وَقَدْ دَخَلَ وَقْتُ الصَّلاَةِ فَلْيُصَلِّ أَرْبَعاً.

He (the Imam) said, ‘He is required to perform his Salah (prayer) as two Rak‘at and if he goes out on a journey when it has become the time for Salah (prayer) he is required to perform his Salah (prayer) as four Rak‘at.’” حسن - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (15/380))