Explanation of the second condition, which is sincerity, and the evidence for it, and explanation of the severity of shirk (associating partners with Allah), whether minor or major.

The Shaykh : And the second condition is that this act, after being in accordance with the Sunnah, must be pure for the sake of Allah (Mighty and Majestic). Because He says at the end of the verse: meaning that one does not intend anything other than the Face of Allah (Mighty and Majestic) with his righteous deed. If he does so, he has associated others with Allah, and his deed is rejected by Him. For Allah, as it came in the authentic hadith: So this deed, however righteous and in accordance with the Sunnah it may be, if it is not pure for the sake of Allah (Mighty and Majestic), it is also rejected. Just as if it were pure for the sake of Allah but not in accordance with the Sunnah, it is likewise rejected. These are two conditions for every righteous deed; if one of them is lacking in it, his deed is not righteous, but rather his deed becomes a burden upon him. It would have been better for him if he had not done it. If a man prayed two rak'ahs at night while people were sleeping, and he prayed them in accordance with the Sunnah without addition or subtraction, but he only sought thereby for people to talk about him and say, "So-and-so is a righteous man who stands in night prayer while people are sleeping," his deed is invalid because he associated people with Allah in this righteous deed. But if his deed were merely invalid and he were not held accountable for it, the apparent meaning of the well-known authentic hadith would be true: The apparent meaning of this is that he lost the deed, but it is not just that; rather, his deed turned into a burden upon him. These two rak'ahs, which we cited as an example of a righteous deed in accordance with the Sunnah when he did not intend the Face of Allah (Mighty and Majestic) in them, are like if he committed a sin among the sins. That is, Allah (Mighty and Majestic) punishes him for these two rak'ahs because he associated with Him (Mighty and Majestic) in them. So one who sleeps and does not pray is better than him, even though he prayed only two rak'ahs. If he prayed eleven rak'ahs and did not add to them in following the Sunnah, but for example he said in his heart, intending in this worship or this obedience to show off to his Salafi brothers, so that his companions would say, "This so-and-so is a Salafi who does not add to the Sunnah," if he intended this intention, his deed is invalid and turns into a burden upon him. He should pray in accordance with the Sunnah, intending thereby purely for the sake of Allah (Mighty and Majestic), not seeking thereby to please people in any way.
This is a brief summary of the speech regarding the deed that does not leave its owner and enters the grave with him. This does not leave him, whether it is a righteous deed or a bad one. But what benefits him is only the righteous deed. What is the righteous deed? What is its condition? Two: that it be in accordance with the Sunnah and that it be pure for the Face of Allah (Blessed and Exalted is He). So remember these two conditions and act upon them so that you may be righteous and successful. The first condition is one that most people are heedless of, rather they are astray from it, because they approve of religious innovation with many claims that we have addressed repeatedly and repeatedly. I do not want to delve into them now.