What is the ruling if one is uncertain about the repeated disturbance of a grave site or the impurity of the dust used for Tayammum?

Primary text

If there is doubt regarding the repeated disturbance of the grave site or regarding the impurity of the dust used for Tayammum, Tayammum is permitted using that dust. This is because the default state (Asl) is purity, and this default is not removed by doubt, similar to the ruling concerning doubt about the purity of water.