Assalaamu 'Alaikum.First of all, thank you for your previous respond. But i have to apologize, this question not about whisper or obsessive doubts, this is about how we act according to a fact, that happens to be has a "real evidence". I have no doubt, i'm really sure about the evidence. The evidence here is very clear and real.Here is the story, i bought a brand new xiaomi redmi 3 smartphone in 2016. But the next year after i checked on government regulations website, my phone was "indeed" proven illegal. Illegal here means imported without any permissions from the government (not stolen, i already know the rules about stolen items). So no doubt about this. I know that some scholars said this act is haram. But not about the case if we didn't know.That leaves the questions:-What is the ruling for anything that we bought, we didn't know it is illegal at the beginning, but then it is proven illegal afterwards? (again, illegal here = "avoid taxes" not stolen items)-Am i allowed to continue using this or should i get rid of it?-What level of investigations should every muslims do for each business transaction like this?I've read your Fatwa No : 352741, in this case, i have a real evidence it is illegal, but the fact that i didn't know at the time i bought it makes me wondering, what is the rulings for this matter. Again, this is not waswaas. I just want to know the ruling in Islam. Fatwa No : 352741 and Fatwa No : 345922 is not suitable for this matter in my opinion.Please give me correct daleel. Thank you very much.Jazak Allahu Khairan Kaseera.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

The information stated in the Fatwa in reference sufficiently underline that there is no religious impediment to availing yourself of the commodity that you had bought while being unaware of the vendor's evasion of the taxes and whether or not he is legislatively obliged to abide by these taxes and accordingly the tax evasion is deemed prohibited in this situation.

In fact, even if you verified his tax evasion, this does not entail deeming it prohibited to buy from him or avail yourself of the purchased commodities. You bear no sin for buying or using this phone even after knowing that vendor evaded taxes; the vendor is the one who bears the sin for such a misdeed and shall bear the legal consequences of his violation of the laws.

It should be noted that a Muslim is not legislatively required to investigate the source of the wealth of each and every person with whom he engages in financial transactions; this incurs serious hardships and difficulties. Rather, he should rely on the basic principle in this regard, namely, the wealth is deemed lawful unless proven otherwise by evidence as long as there are no valid reasons calling for any further investigation and refraining from the engagement in any given financial transaction with that person.

Shaykhul-Islam Ibn Taymiyyah said, “If the person does not know how this man earned his wealth, what is unknown is effectively the same as what is non-existent. (According to Islamic Shareeʻah, the unknown is similar to the non-existent.) The basic principle is that whatever is in the possession of the Muslim and he claims to be his is considered his property. As long as I do not know the source of the person's wealth, I should rely on the fundamental principle in this regard. If this person has actually usurped and unlawfully seized this property, but I do not know that, it is deemed his property (by me); what is unknown is effectively the same as what is non-existent. However, if this man is known for earning his wealth through unlawful means, the Muslim should refrain from dealing with him out of religious prudence and consciousness of Allah. As for the person whose wealth is mostly unlawful, the scholars have held different opinions about it. As for the transactions with a Muslim man the source of whose wealth is unknown, there is no doubt about the permissibility of engaging in financial transactions with him as a fundamental rule. If the person refrains from dealing with such a Muslim out of religious prudence, he has committed a religious innovation that has nothing to do with what Allah has revealed.” [Majmooʻ Al-Fataawa: Excerpted with slight modifications]

Allah Knows best.