Is it prohibited to use the right hand for Istijmar with stones?
Chapter on Cleaning oneself (Istitabah) and Impurity (Hadath)
Al-Mughni
Book of Purification
Primary text
It is prohibited to use the right hand for Istijmar, based on Salman's narration that the Prophet (PBUH) forbade cleansing with the right hand, and Abu Qatadah's narration that the Prophet (PBUH) forbade touching the private parts with the right hand or cleansing with it after excretion. If cleansing from feces, the stone should be held with the left hand. If cleansing from urine and the stone is large, the penis should be held with the left hand while wiping with the stone. If the stone is small, one should place it between the buttocks or fingers and wipe, or hold the penis with the right hand and wipe with the left to ensure the wiping action is done by the left hand.
Supporting text
If one is left-handed (missing the left hand) or has an illness affecting the left hand, Istijmar is performed with the right hand out of necessity. If one uses the right hand for Istijmar while having the means to avoid it, the majority of scholars state it is nevertheless valid (جزأه). Some scholars of Al-Zahiriyyah hold that it is invalid because it is explicitly forbidden, akin to using dung or dried dung (rima). The counterargument is that the hand itself is not the direct agent touching the impurity; rather, it handles the stone, making the prohibition one of etiquette (ta'deeb) that does not invalidate the act.