1 Samuel 13:12 (KJV)

And it came to pass, that as soon as he had made an end of offering the burnt offering, behold, Samuel came; and Saul went out to meet him, that he might salute him.

And Samuel said, What hast thou done? And Saul said, Because I saw that the people were scattered from me, and that thou camest not within the days appointed, and that the Philistines gathered themselves together at Michmash;

Therefore said I, The Philistines will come down now upon me to Gilgal, and I have not made supplication unto the Lord: I forced myself therefore, and offered a burnt offering.

And Samuel said to Saul, Thou hast done foolishly: thou hast not kept the commandment of the Lord thy God, which he commanded thee: for now would the Lord have established thy kingdom upon Israel for ever.

But now thy kingdom shall not continue: the Lord hath sought him a man after his own heart, and the Lord hath commanded him to be captain over his people, because thou hast not kept that which the Lord commanded thee.