What is incumbent upon one who has prayed for two days, forgetting that he was in a state of ritual impurity (junub), and what is the evidence for that?

A Muslim must make up prayers performed while in a state of major ritual impurity (janabah), because purity is a condition for the validity of prayer. This is based on the Prophet, peace and blessings be upon him, who said: "No prayer is accepted without purification." What is meant by "accepted" here is "valid." He must hasten to make them up in their proper order.