Rashi on Numbers 16:25/רש"י על במדבר ט״ז:כ״ה

1ויקם משה AND MOSES ROSE UP [AND WENT UNTO DATHAN AND ABIRAM] — He still believed that they would show respect to him (defer to him if he personally appealed to them), but they did not do so, (and therefore he then addressed himself to all the congregation — cf. next verse) (Midrash Tanchuma, Korach 8).