Explaining that an act of worship is not valid unless two conditions are met: sincerity and following the Prophet.

The Shaykh : Know that an act of worship cannot be valid unless two things are present in it. The first thing is sincerity for Allah (Mighty and Majestic). Sincerity for Allah means that you do not intend by your worship to be praised by people, or to be prominent among them, or to be honored in their eyes. You intend in your worship only the Face of Allah and the Hereafter, and you do not care whether people see you or not, because you know for whom you are working: for Allah. This is sincerity. The sign of sincerity is that when a person performs an act of worship, there is no difference for him between people knowing about it or not knowing about it. This is the sincere person who says, "It does not matter to me, it does not matter to me. I worship Allah whether people know that I worship Allah or they do not know, and whether they see me or they do not see me." This is the sign of sincerity.