مُوَطَّأُ مَالِكٍ
Muwatta Malik 465
The Qibla
حَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّ عُمَرَ بْنَ الْخَطَّابِ، قَالَ مَا بَيْنَ الْمَشْرِقِ وَالْمَغْرِبِ قِبْلَةٌ إِذَا تُوُجِّهَ قِبَلَ الْبَيْتِ .
Yahya related to me from Malik from Nafi that Umar ibn al-Khattab said, "Any direction that is between east and west can be taken as a qibla if the person praying is face-on to the House."
Arabic/English book reference: Book 14, Hadith 8