First thing, there is no concept of inherited sin in Islam. We are born without any sin or sinful conditions. Similarly if a child is born with any abnormal conditions, it is not a punishment of any sin of parents or forefathers.
The purification of one’s self is very difficult and yet salvation is based on the purification of self. God the Almighty says: Qad aflaha man zakkaaha; that is to say, he who purifies himself attains to success. But the purification cannot be attained to except with the grace of God. The inviolable law of God