وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ الْقَاسِمَ بْنَ مُحَمَّدٍ، وَعُرْوَةَ بْنَ الزُّبَيْرِ، وَأَبَا، بَكْرِ بْنَ عَبْدِ الرَّحْمَنِ كَانُوا يَتَنَفَّلُونَ فِي السَّفَرِ ‏.‏ قَالَ يَحْيَى وَسُئِلَ مَالِكٌ عَنِ النَّافِلَةِ فِي السَّفَرِ فَقَالَ لاَ بَأْسَ بِذَلِكَ بِاللَّيْلِ وَالنَّهَارِ وَقَدْ بَلَغَنِي أَنَّ بَعْضَ أَهْلِ الْعِلْمِ كَانَ يَفْعَلُ ذَلِكَ ‏.‏

Yahya related to me from Malik that he had heard that al-Qasimibn Muhammad and Urwa ibn az-Zubayr and Abu Bakr ibn Abd ar Rahmanused to pray nawafil when travelling. Yahya said that Malikwas asked about voluntary prayers when travelling and he said, "Thereis no harm in them, either at night or during the day. I have heardthat some of the people of knowledge used to do that." Translation Not Available

Book Ref: Muwatta Imam Malik Book 9 Hadith 354
Web Ref:  Muwatta Imam Malik Book 9 Hadith 25