My father ordered a product online which costs around 7000 Indian Rupees. But somehow he got it for just 100 Indian Rupees. I know he is sinful. My question is if I use that product would I be sinful?

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.

If your father cheated in taking the product without right, then you have to order him to return it to its owner along with repenting to Allah. If he does not return it to its owner, it is not permissible for you to use it, otherwise you will be sharing the sin.

‘Ileesh [from the Maalik School of jurisprudence], said in his Fataawa:

“Its text [i.e. of Imaam Maalik] is a matter in dealing with the people who have earned ill-gotten money (forbidden income), and their money is divided into two categories:

One of them: is when what is forbidden exists in-kind with the usurper or thief, and the like; it is neither permissible to buy it from him, nor to sell it if it is in-kind, nor to eat it if it is food, nor to wear it if it is a dress, nor to accept anything from that as a gift, nor to take it in return for a debt; and whoever does anything of that, he is like the usurper, in a way that he has handled what is forbidden with his own hands, and he is liable for it.”

Allah knows best.