Hawzah News Agency – The sun can purify an impure ḥaṣīr or mat; but if it is woven with thread, the sun does not purify the threads. To say that trees, grass, doors, and windows become pure by means of the sun is problematic [i.e. based on obligatory precaution, they do not become pure in this way].
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. And if a person doubts whether or not something prevented the sun from shining on the impure object, then to consider it as having become pure is problematic [i.e. based on obligatory precaution, it must not be considered as having become pure].
If the sun shines on one side of an impure wall and as a result the other side of the wall – on which the sun did not shine – also becomes dry, it is not farfetched (baʿīd)(1) to consider both sides as having become pure [i.e. both sides are deemed to be pure]. However, if one day the sun dries the exterior of a wall or some earth and another day its interior, then only its exterior becomes pure.
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(1) For practical purposes, a legal opinion that is termed ‘not farfetched’ equates to a fatwa.