The Book of Prayer
Bulugh al-Maram #255
كتاب الصلاة
وَلِأَبِي دَاوُدَ: مِنْ حَدِيثِ أَنَسٍ: «كَانَ إِذَا سَافَرَ فَأَرَادَ أَنْ يَتَطَوَّعَ اِسْتَقْبَلَ بِنَاقَتِهِ اَلْقِبْلَةِ, فَكَبَّرَ, ثُمَّ صَلَّى حَيْثُ كَانَ وَجْهَ رِكَابِهِ» وَإِسْنَادُهُ حَسَنٌ.
Narrated Anas in another narration of the Hadith reported by Abu Dawud:
When traveled, and intended to pray a voluntary prayer, he used to direct his riding camel towards the Qiblah, say, “Allahu Akbar” and pray facing whatever direction it faced.
وَلِأَبِي دَاوُدَ : مِنْ حَدِيثِ أَنَسٍ : "كَانَ إِذَا سَافَرَ فَأَرَادَ أَنْ يَتَطَوَّعَ اِسْتَقْبَلَ بِنَاقَتِهِ اَلْقِبْلَةِ , فَكَبَّرَ , ثُمَّ صَلَّى حَيْثُ كَانَ وَجْهَ رِكَابِهِ" وَإِسْنَادُهُ حَسَنٌ .
When traveled, and intended to pray a voluntary prayer, he used to direct his riding camel towards the Qiblah, say, "Allahu Akbar" and pray facing whatever direction it faced.
— Bulugh al-Maram, Hadith 255