Sunan Ibn Majah 614
It was narrated that 'Abdullah bin Harith bin Nawfal said:
"I asked whether the Messenger of Allah prayed voluntary prayer when traveling, but I could not find anyone to tell me until Umm Hani' bint Abu Talib told me that he had come during the year of the Conquest (of Makkah). He ordered that a screen be held up, and that was done, and he took a bath; then he prayed eight Rak'ah (units) of voluntary prayer."
حَدَّثَنَا مُحَمَّدُ بْنُ رُمْحٍ الْمِصْرِيُّ، أَنْبَأَنَا اللَّيْثُ بْنُ سَعْدٍ، عَنِ ابْنِ شِهَابٍ، عَنْ عَبْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ بْنِ نَوْفَلٍ، أَنَّهُ قَالَ سَأَلْتُ فَلَمْ أَجِدْ أَحَدًا يُخْبِرُنِي أَنَّ رَسُولَ اللَّهِ ـ صلى الله عليه وسلم ـ سَبَّحَ فِي سَفَرٍ حَتَّى أَخْبَرَتْنِي أُمُّ هَانِئٍ بِنْتُ أَبِي طَالِبٍ أَنَّهُ قَدِمَ عَامَ الْفَتْحِ فَأَمَرَ بِسِتْرٍ فَسُتِرَ عَلَيْهِ فَاغْتَسَلَ ثُمَّ سَبَّحَ ثَمَانِيَ رَكَعَاتٍ ‏.‏