Hadith 504650
Chapter 14: The Qibla - كتاب القبلة
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."
Reference Muwatta Malik 504650
USC-MSA web (English) reference : Book 14, Hadith 8