'Commandment of the Lord' in the Bible

Then said Samuel to Saul, "Thou hast done foolishly and hast not kept the commandment of the LORD thy God which he commanded thee. For at this time would the LORD have established thy kingdom upon Israel forever.

And when Samuel was come to Saul, Saul said unto him, "Blessed be thou in the LORD. I have done the commandment of the LORD."