Not offering As-Salat (the prayers) at its stated fixed time
حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، قَالَ حَدَّثَنَا مَهْدِيٌّ، عَنْ غَيْلاَنَ، عَنْ أَنَسٍ، قَالَ مَا أَعْرِفُ شَيْئًا مِمَّا كَانَ عَلَى عَهْدِ النَّبِيِّ صلى الله عليه وسلم. قِيلَ الصَّلاَةُ. قَالَ أَلَيْسَ ضَيَّعْتُمْ مَا ضَيَّعْتُمْ فِيهَا.
Narrated Ghailan: Anas said, "I do not find (now-a-days) things as they were (practiced) at the time of the Prophet." Somebody said "The prayer (is as it was.)" Anas said, "Have you not done in the prayer what you have done?