Hadith 504240
Chapter 9: Shortening the Prayer - كتاب قصر الصلاة فى السفر
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 .
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."
Reference Muwatta Malik 504240
USC-MSA web (English) reference : Book 9, Hadith 92