I say, and with God's success: Istinja (cleaning after relieving oneself) is either obligatory: if the impurity is more than the size of a dirham, or required: if the impurity is the size of a dirham, or a Sunnah: if the impurity is less than the size of a dirham, or recommended: if one has urinated but not defecated, then he washes his front without washing his back. Or as a precaution: if something comes out from his body and does not soil him, he washes that area as a precaution, or it is an innovation: if something comes out from other than the two passages, or if gas is released from his back, then he does not perform istinja, and if he does, that would be an innovation. Refer to: Al-Tawdeeh Sharh Muqaddimah Abi Al-Layth 94/b, Bada'i Al-Sana'i 1/18, Al-Ikhtiyar 1/48, and God knows best.