Be careful when you speak against a servant of God. He does not take kindly to such idle talk. For instance, Miriam and Aaron spoke against Moses because of his wife. Maybe she had more influence over him than they did, and perhaps they resented her. God became furious with them and called them to the tabernacle's door, rebuking them in front of Moses. God reminded them that he spoke to Moses face to face, but to them, he appeared in dreams and visions. It seems that Miriam was the one who led this rebellion because God struck her with leprosy while Aaron begged for Moses to heal her. Moses cried out to God, but he made her live with the leprosy outside of camp for seven days, which must have been humbling for her.
Here's a bit of caution: if God's servant says something you disagree with, hold your peace and take your issue directly to God unless it is entirely egregious and not biblical. Yes, we should take a stand against false prophets, but just be careful who you criticize. God hears our words and thoughts; make sure you take every word and thought captive, making them obedient to Christ.
With him will I speak mouth to mouth, even apparently, and not in dark speeches; and the similitude of the LORD shall he behold: wherefore then were ye not afraid to speak against my servant Moses? And the anger of the LORD was kindled against them; and he departed. Numbers 12:8-9