Mishkat al-Masabih
Mishkat al-Masabih 1353
Prayer while Travelling - Section 3
Arabic hadith text
وَعَنْ نَافِعٍ قَالَ: إِنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ كَانَ يَرَى ابْنَهُ عُبَيْدَ اللَّهِ يَتَنَفَّلُ فِي السَّفَرِ فَلَا يُنْكِرُ عَلَيْهِ. رَوَاهُ مَالِكٌ
Translation
Nafi' said that ‘Abdallah b. ‘Umar used to see his son ‘Ubaidallah saying supererogatory prayers while on a journey, and did not express disapproval. Malik transmitted it.