What is the ruling on expelling water from the nose with the right hand after sniffing water into it during wudu?

The Sunnah is to perform istinthar (expelling water from the nose) with the left hand, which is done to remove impurities from the nose. This is supported by the hadith of Ali (may Allah be pleased with him): "that he called for water for ablution, then rinsed his mouth, inhaled water, and expelled it with his left hand." The general rule is that the right hand is for honorable acts, and the left hand is for acts involving impurities.