Due to the ignorance of some Muslims regarding the phrase "La ilaha illa Allah," they have fallen into shirk (associating partners with Allah) through slaughtering for other than Allah and making vows for other than Allah.

The Shaykh : This is because they do not know the meaning of "La ilaha illa Allah" as the polytheists knew it. Regrettably, the polytheists knew the reality of "La ilaha illa Allah," so they disbelieved and denied it, as you heard in the previous verses. But our Muslim brothers, these people, bear witness with complete sincerity to "La ilaha illa Allah, Muhammad is the Messenger of Allah." However, regrettably, due to their distance from the Arabic language on one hand, and their distance from seeking religious knowledge on the other, they do not know the meaning of "La ilaha illa Allah" as those polytheists knew it. To show the difference between them and those polytheists: the polytheists understood it and disbelieved, while these people disbelieved without knowing it. This is very strange. These Muslims, whom we cite as examples, who slaughter for other than Allah and make vows for other than Allah, are different from the polytheists in one respect and similar to them in another. They differ from the polytheists in that the polytheists were better than them in understanding; they understood that the meaning of "La ilaha illa Allah" necessitates the oneness of Allah in worship, but they disbelieved in this meaning they understood. As for the Muslims today, except for those whom Allah wills, they did not understand this understanding that the first Arab polytheists had of this good word. Then they participated with them in what the Arabs disbelieved in regarding the oneness of Allah in worship. So they began to do what the ancient Arabs did. What did the Arabs do? They slaughtered for their idols and made vows for their idols. This slaughtering for their idols and these vows for their idols is the worship that the Arabs directed to other than Allah, to these idols, so they disbelieved...
Zakariyya, we have in Damascus, Sham, Yahya; this one is called there... other than Allah, and there he is called other than Allah. All of this is worship of other than Allah, Mighty and Majestic. But most people, as our Lord said, do not know. What is worship? It is directing any worship, whatever it is, that Allah has commanded you to submit to Him with, and to worship Him and not worship anyone else with it in it. And if you direct this worship to these awliya (close friends of Allah) and the righteous, thereby you worship other than Allah, Mighty and Majestic. Our Lord, Mighty and Majestic, says: meaning my worship, my standing... and my prostration, my supplication; all of this is called prayer. For whom is this prayer? He said: for Allah . What is the sacrifice (nasik)? The sacrifice is the animals that are slaughtered and with which one draws near to Allah, Blessed and Exalted is He. And ignorance leads many Muslims to direct their prayer, to direct their supplication to other than Allah, Mighty and Majestic, to direct their sacrifices to other than Allah, Mighty and Majestic, to the point of directing their supplication to say, "O Allah, help me," instead of saying, "O Abu al-Zuhra, help me"... And there are many, many anthems, all of which are calls for aid to other than Allah, Mighty and Majestic. This is practical disbelief in the meaning of "La ilaha illa Allah," because the meaning, as you heard, is that there is no deity worthy of worship in existence except Allah. And yet they worship other than Allah without right.