Sahih Muslim 85
Sahih Muslim · Book 1: The Book of Faith · Clarifying that faith in Allah most high is the best of deeds
It is reported on the authority of 'Abdullah that the Messenger of Allah observed:
حَدَّثَنَا عُثْمَانُ بْنُ أَبِي شَيْبَةَ ، حَدَّثَنَا جَرِيرٌ ، عَنِ الْحَسَنِ بْنِ عُبَيْدِ اللَّهِ ، عَنْ أَبِي عَمْرٍو الشَّيْبَانِيِّ ، عَنْ عَبْدِ اللَّهِ ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " أَفْضَلُ الأَعْمَالِ - أَوِ الْعَمَلِ - الصَّلاَةُ لِوَقْتِهَا وَبِرُّ الْوَالِدَيْنِ " .
The best of' the deeds or deed is the (observance of) prayer at its proper time and kindness to the parents.