مُوَطَّأُ مَالِكٍ
Muwatta Malik 348
Shortening the Prayer
حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ عَطَاءٍ الْخُرَاسَانِيِّ، أَنَّهُ سَمِعَ سَعِيدَ بْنَ الْمُسَيَّبِ، قَالَ مَنْ أَجْمَعَ إِقَامَةً أَرْبَعَ لَيَالٍ وَهُوَ مُسَافِرٌ أَتَمَّ الصَّلاَةَ . قَالَ مَالِكٌ وَذَلِكَ أَحَبُّ مَا سَمِعْتُ إِلَىَّ . وَسُئِلَ مَالِكٌ عَنْ صَلاَةِ الأَسِيرِ فَقَالَ مِثْلُ صَلاَةِ الْمُقِيمِ إِلاَّ أَنْ يَكُونَ مُسَافِرًا .
Yahya related to me from Malik from Ata al-Khurasani that he heard Said ibn al Musayyab say, "A traveller who has decided to remain somewhere for four nights does the prayer in full." Malik said, "That is what I prefer most out of what I have heard." Malik when asked about the prayer of a prisoner, said, "It is the same as the prayer of a person who remains in one place, except if he is travelling."
Arabic/English book reference: Book 9, Hadith 20