All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The hand with which one has performed Istinjaa’ (cleaning oneself using water after answering the call of nature), is not always considered impure; rather, it is considered pure if there is no trace of impurity left on it (its color or smell), but it is desirable to wash it after cleaning oneself with soil and the like of it such as soap to remove dirt from it.
Maymoonah narrated about the manner of the Prophet when performing Istinjaa’, saying: “Then he struck the ground with his hand and rubbed it very hard.”
“This Hadeeth indicates that it is desirable for the one who has cleansed himself (performed Istinjaa’) with water, when he has finished, to wash his hand with soil or a plant (that produces something like soap), or to rub it with soil, or against the wall, to remove dirt from it.” [End of quote]
Al-Kharshi ‘ala Mukhtasar Khaleel, in the Maliki School of jurisprudence, reads: “It is also recommended to wash the hand after Istinjaa’ with soil or sand or the like, which removes the smell.” [End of quote]
Allah knows best.