1 Samuel 12:16-18

So now, take your stand and see this great thing which the LORD will do before your eyes. Is it not [the beginning of the] wheat harvest today? I will call to the LORD and He will send thunder and rain; then you will know [without any doubt], and see that your evil which you have done is great in the sight of the LORD by asking for yourselves a king.” So Samuel called to the LORD [in prayer], and He sent thunder and rain that day; and all the people greatly feared the LORD and Samuel.