Purity: Ruling on Doubt Concerning Purification by the Sun

Practical Laws of Islam as per the teachings of Ayatullah Sistani

Ruling 187

If the sun shines on impure earth and afterwards a person doubts whether or not the earth was wet when the sun shone on it, or whether or not the wetness of the earth has dried by means of the sun, then that earth is impure. The same applies if one doubts whether or not the intrinsic impurity has been removed. If a person doubts whether or not something prevented the sun from shining on the impure object, then based on obligatory precaution, it must not be considered pure.

-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)