Is it a condition for the validity of wudu' that the ground we perform wudu' on be pure and not ritually impure?

It is not a condition for the validity of ablution (wudu') to perform it in a pure place. So, whoever performs ablution in an impure place has acted contrary to what is preferable, but their ablution is valid. Some books of the Maliki and Hanafi schools mentioned the desirability of performing ablution in a pure place, because the water used for ablution has sanctity.