Some people say that all Muslims are disbelievers, even if they declare the Two Testimonies of Faith, simply because they do some acts that result in disbelief while they are not aware of its impermissibility. Please advise.

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

People of knowledge should raise public awareness on matters of ‘Aqeedah, so that others might not commit acts that result in disbelief. Muslims should be keen on learning such things. They should say this Du‘aa’ (Supplication),  "Allaahumma inni a‘oothu bika an ushrika bika wa ana a‘lam wa astaghfiruka li maa laa a‘lam (O Allaah, make me not associate anything with You while being aware of doing so, and I ask You to forgive me if I associate anything with You, while not being aware of doing so.)" [Al-Bukhari in Al-Adab  Al-Mufrad]  Al-Albaani declared this Hadeeth as Saheeh (Authentic).

The Messenger of Allaah, sallallaahu ‘alayhi wa sallam, told Abu Bakr that a person may commit Shirk (polytheism) without being aware that he is doing so, and then he, sallallaahu ‘alayhi wa sallam, advised Abu Bakr to say the aforementioned Du‘aa’.

Allaah Knows best.