What is the ruling on the ablution of one who used to wash up to part of the shin due to ignorance of the boundaries of ablution?

If a person washes an additional part of the leg or more than what is required for the rest of the ablution organs, then their ablution is valid. In fact, this action is considered better by some scholars who deem it desirable to lengthen the "ghurrah" (the white blaze on the forehead of a horse, metaphorically referring to the traces of ablution). It is incumbent upon a Muslim to learn the rulings of individual obligations like prayer and ablution, for learning what is obligatory is an obligation, and what is necessary is necessary.