Samuel asked Saul that question. Samuel had not shown up at the designated time before the battle to offer the sacrifice. Therefore, Saul did it himself,

And Samuel said,

“What have you done?” Saul said, “When I saw that the people were scattered from me, and that you did not come within the days appointed, and that the Philistines gathered together at Michmash, then I said, ‘The Philistines will now come down on me at Gilgal, and I have not made supplication to the Lord.’ Therefore I felt compelled, and offered a burnt offering” (1 Samuel 13:11–12).

He said that he felt compelled, but that compelling did not come from the Lord, the Holy Spirit, or anything from heaven. It was Saul’s own heart. He followed his feelings and it got him into trouble, as Solomon said,

He who trusts in his own heart is a fool,
But whoever walks wisely will be delivered.
(Proverbs 28:26)