Muwatta Malik, Book 9, Hadith 92 (USC-MSA)

Yahya related to me from Malik that Yahya ibn Said said, "I have heard that the first of the actions of a slave to be considered on the day of rising is the prayer. If it is accepted from him, the rest of his actions will be considered, and if it is not accepted from him, none of his actions will be considered."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، أَنَّهُ قَالَ بَلَغَنِي أَنَّ أَوَّلَ، مَا يُنْظَرُ فِيهِ مِنْ عَمَلِ الْعَبْدِ الصَّلاَةُ فَإِنْ قُبِلَتْ مِنْهُ نُظِرَ فِيمَا بَقِيَ مِنْ عَمَلِهِ وَإِنْ لَمْ تُقْبَلْ مِنْهُ لَمْ يُنْظَرْ فِي شَىْءٍ مِنْ عَمَلِهِ ‏.‏

sunnah.com

also referenced under: Book 9, Hadith 424 (In-Book)

Yahya related to me from Malik from Hisham ibn Urwa from his father that A'isha, the wife of the Prophet, may Allah bless him and grant him peace, said, "The actions which the Messenger of Allah, may Allah bless him and grant him peace, loved most were those which were done most constantly."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، زَوْجِ النَّبِيِّ صلى الله عليه وسلم أَنَّهَا قَالَتْ كَانَ أَحَبُّ الْعَمَلِ إِلَى رَسُولِ اللَّهِ صلى الله عليه وسلم الَّذِي يَدُومُ عَلَيْهِ صَاحِبُهُ ‏.‏

sunnah.com

also referenced under: Book 9, Hadith 425 (In-Book)