Sahih Muslim , Book 15, Hadith 253 (In-Book) ⓘ

Nafi' reported that Abdullah (b. 'Umar) informed him that Allah's Messenger turned his face to the two hillocks which intervened between him and the long mountain by the side of the Ka'ba, and the mosque which had been built there was thus on the left of the hillock. Allah's Messenger's place of prayer was lower than the black hillock, at a distance of ten cubits or near it. He would then observe prayer facing these two hillocks of the long mountain that is intervening between you and the Ka'ba.

حَدَّثَنَا مُحَمَّدُ بْنُ إِسْحَاقَ الْمُسَيَّبِيُّ، حَدَّثَنِي أَنَسٌ، - يَعْنِي ابْنَ عِيَاضٍ - عَنْ مُوسَى، بْنِ عُقْبَةَ عَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ، أَخْبَرَهُ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم اسْتَقْبَلَ فُرْضَتَىِ الْجَبَلِ الَّذِي بَيْنَهُ وَبَيْنَ الْجَبَلِ الطَّوِيلِ نَحْوَ الْكَعْبَةِ يَجْعَلُ الْمَسْجِدَ الَّذِي بُنِيَ ثَمَّ يَسَارَ الْمَسْجِدِ الَّذِي بِطَرَفِ الأَكَمَةِ وَمُصَلَّى رَسُولِ اللَّهِ صلى الله عليه وسلم أَسْفَلَ مِنْهُ عَلَى الأَكَمَةِ السَّوْدَاءِ يَدَعُ مِنَ الأَكَمَةِ عَشْرَ أَذْرُعٍ أَوْ نَحْوَهَا ثُمَّ يُصَلِّي مُسْتَقْبِلَ الْفُرْضَتَيْنِ مِنَ الْجَبَلِ الطَّوِيلِ الَّذِي بَيْنَكَ وَبَيْنَ الْكَعْبَةِ صلى الله عليه وسلم ‏.‏