Al-Kāfi - Volume 3 > Where to Apply Rules about Salah (Prayer) on a Journey
Hadith #7

7ـ عَلِيُّ بْنُ إِبْرَاهِيمَ عَنْ أَبِيهِ عَنْ حَمَّادٍ عَنْ حَرِيزٍ عَنْ زُرَارَةَ قَالَ قُلْتُ لَهُ رَجُلٌ فَاتَتْهُ صَلاَةٌ مِنْ صَلاَةِ السَّفَرِ فَذَكَرَهَا فِي الْحَضَرِ قَالَ يَقْضِي مَا فَاتَهُ كَمَا فَاتَهُ إِنْ كَانَتْ صَلاَةَ السَّفَرِ أَدَّاهَا فِي الْحَضَرِ مِثْلَهَا وَإِنْ كَانَتْ صَلاَةَ الْحَضَرِ فَلْيَقْضِ فِي السَّفَرِ صَلاَةَ الْحَضَرِ كَمَا فَاتَتْهُ.

7. Ali ibn Ibrahim has narrated from his father from Hammad from Hariz from Zurarah who has said the following: “I once asked him (the Imam), ‘Alayhi al-Salam, about a man who misses a Salah (prayer) while on a journey and remembers it when he is at home. He (the Imam) said, ‘He performs Qada’ (compensatory prayer) for it just as it was missed, if missed on a journey the compensatory prayer for it at home is as reduced and if it is missed at home the compensatory prayer for it, if performed on a journey, is complete.’”