Al-Kāfi - Volume 3 > Required Length of Distance of a Journey for Shortened Salah (Prayer)
Hadith #4

4ـ عَلِيُّ بْنُ إِبْرَاهِيمَ عَنْ أَبِيهِ عَنِ ابْنِ أَبِي عُمَيْرٍ عَنْ بَعْضِ أَصْحَابِهِ عَنْ أَبِي عَبْدِ الله (عَلَيْهِ الْسَّلام) قَالَ سُئِلَ عَنْ حَدِّ الأمْيَالِ الَّتِي يَجِبُ فِيهَا التَّقْصِيرُ فَقَالَ أَبُو عَبْدِ الله (عَلَيْهِ الْسَّلام) إِنَّ رَسُولَ الله (صلّى اللهُ عَلَيْهِ وَآلِه) جَعَلَ حَدَّ الأمْيَالِ مِنْ ظِلِّ عَيْرٍ إِلَى ظِلِّ وُعَيْرٍ وَهُمَا جَبَلاَنِ بِالْمَدِينَةِ فَإِذَا طَلَعَتِ الشَّمْسُ وَقَعَ ظِلُّ عَيْرٍ إِلَى ظِلِّ وُعَيْرٍ وَهُوَ الْمِيلُ الَّذِي وَضَعَ رَسُولُ الله (صلّى اللهُ عَلَيْهِ وَآلِه) عَلَيْهِ التَّقْصِيرَ.

4. Ali ibn Ibrahim has narrated from his father from ibn abu ‘Umayr from certain persons of our people who has said the following: “Abu ‘Abd Allah, ‘Alayhi al-Salam, was asked about the limit of the miles which is involved in Taqsir (reducing Salah (prayer) on a journey after traveling a certain distance). Abu ‘Abd Allah, ‘Alayhi al- Salam, said, ‘The Messenger of Allah had determined the limits of such mile to be from the shadow of ‘Ayr to the shadow of O’ Ayr and they are two mountains in al-Madinah. On sunrise the shadow of ‘Ayr falls on the shadow of O’ Ayr and that is the mile that the Messenger of Allah had set up for Taqsir (reducing Salah (prayer) on a journey after traveling a certain distance).”’