وَحَدَّثَنَا يَحْيَى بْنُ يَحْيَى، قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنِ ابْنِ عُمَرَ، أَنَّهُ قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُصَلِّي عَلَى رَاحِلَتِهِ حَيْثُمَا تَوَجَّهَتْ بِهِ ‏.‏ قَالَ عَبْدُ اللَّهِ بْنُ دِينَارٍ كَانَ ابْنُ عُمَرَ يَفْعَلُ ذَلِكَ ‏.‏

'Abdullah b. Dinar reported on the authority of Ibn 'Umar that the Messenger of Allah (PBUH) used to observe prayer on his ride (no matter) in which direction it had its face turned. 'Abdullah b. Dinar said that Ibn 'Umar used to do like that. Translation Not Available

Book Ref: Sahih Muslim Book 6 Hadith 1503
Web Ref:  Sahih Muslim Book 4 Hadith 700 g