So Moses cried out to the LORD, "O God, please heal her!" ~~ Numbers 12:13 (NIV)
Recorded in Numbers 12 for us to know for all time, God spoke to Moses face to face. Moses was the most humble man on all the earth.
When Miriam received her punishment of leprosy for speaking against her brother, Moses cried out to the Lord on her behalf.
In the Hebrew, the word for cried is “Tsa`aq” which means “to cry, to cry out (for help) or (in distress or need). 
Moses felt deep despair over what happened to his sister and wanted help. He cried out to the only One who could heal her, the Lord. I like how Matthew Henry’s Commentary explains Moses in this situation:
"III. The intercession made for Miriam (v. 13): He cried unto the Lord with a loud voice, because the cloud, the symbol of his presence, was removed and stood at some distance, and to express his fervency in this request, Heal her now, O Lord, I beseech thee. By this he made it to appear that he did heartily forgive her the injury she had one him, that he had not accused her to God, nor called for justice against her; so far from this that, when God in tenderness to his honour had chastised her insolence, he was the first that moved for reversing the judgment. By this example we are taught to pray for those that despitefully use us; and not to take pleasure in the most righteous punishment inflicted either by God or man on those that have been injurious to us. Jeroboam’s withered hand was restored at the special instance and request of the prophet against whom it had been stretched out, 1 Ki. 13:6. So Miriam here was healed by the prayer of Moses, whom she had abused, and Abimelech by the prayer of Abraham, Gen. 20:17. Moses might have stood off, and have said, "She is served well enough, let her govern her tongue better next time;’’ but, not content with being able to say that he had not prayed for the inflicting of the judgment, he prays earnestly for the removal of it. This pattern of Moses, and that of our Saviour, Father, forgive them, we must study to conform to."
Matthew Henry’s goes on to explain that mercy and justice both met Miriam. Mercy in that Miriam did receive healing, forgiveness and God’s will to restore her. Justice in the fact she was put outside the camp for seven days. Yet the process of mercy started when Moses immediately forgave her and cried out.