The ruling on ritual impurity when it falls on the one praying

Question:
If ritual impurity falls on the one praying, and he is unable to remove it?

Answer:
He is unable to, but this was in the early period of Islam, before the migration. He is able to remove it.
Q: If a child urinates on him while he is in prostration?
The Shaykh: The prayer becomes invalid. He stands up and washes the ritual impurity that affected him.
But this was in the early period of Islam; the rulings came after that.