Exodus 2:11

Moses became aware of the suffering of his people under Egyptian rule. Exodus 2:11 tells the story:

He (Moses) saw an Egyptian beating a Hebrew, one of his kinsmen. And he looked this way and that way, and when he saw that there was no man, he smote the Egyptian and hid him in the sand.

After this Moses fled Egypt. His journey brought him to the House of Jethro, the High Priest of Midian.