What is the ruling on sniffing water into the nose (istinshaq) and expelling it (istinthaar) with the left hand during wudu?

Using the right hand for rinsing the mouth (madmadah) is preferable, and for expelling water from the nose (istinshar) with the left hand. The proof for this is what was narrated from Uthman, may Allah be pleased with him, that he performed ablution, so he scooped with his right hand and rinsed his mouth and sniffed water into his nose, then expelled it with his left hand. Al-Kasani mentioned that rinsing the mouth is with the right hand and expelling water from the nose is with the left hand because the mouth is a place of purification and the nose is a place of impurities, and the right hand is for pure things while the left hand is for impure things.