وَحَدَّثَنِي عَنْ مَالِك ، قَالَ: بَلَغَنِي ، عَنْ نَافِعٍ ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ كَانَ يَرَى ابْنَهُ عُبَيْدَ اللَّهِ بْنَ عَبْدِ اللَّهِ يَتَنَفَّلُ فِي السَّفَرِ فَلَا يُنْكِرُ عَلَيْهِ
It is narrated from Hazrat Nafi that Sayyiduna Abdullah bin Umar (may Allah be pleased with them) used to see his son Ubaidullah performing voluntary prayers during travel, and he would not object to him for this.