Sunan Ibn Majah, Book 5, Hadith 1133 (In-Book) ⓘ
It was narrated from Anas bin Malik that the Prophet said: “There is nothing standing between a person and Shirk (polytheism) except leaving the prayer, so if he leaves it he has committed Shirk.”
حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ إِبْرَاهِيمَ الدِّمَشْقِيُّ، حَدَّثَنَا الْوَلِيدُ بْنُ مُسْلِمٍ، حَدَّثَنَا الأَوْزَاعِيُّ، عَنْ عَمْرِو بْنِ سَعْدٍ، عَنْ يَزِيدَ الرَّقَاشِيِّ، عَنْ أَنَسِ بْنِ مَالِكٍ، عَنِ النَّبِيِّ ـ صلى الله عليه وسلم ـ قَالَ " لَيْسَ بَيْنَ الْعَبْدِ وَالشِّرْكِ إِلاَّ تَرْكُ الصَّلاَةِ فَإِذَا تَرَكَهَا فَقَدْ أَشْرَكَ " .
also referenced under: Hadith 1080 (Reference) & Volume 2, Book 5, Hadith 1080 (DarusSalam)