2 Samuel 24:10 (KJV)

So when they had gone through all the land, they came to Jerusalem at the end of nine months and twenty days.

And Joab gave up the sum of the number of the people unto the king: and there were in Israel eight hundred thousand valiant men that drew the sword; and the men of Judah were five hundred thousand men.

And David’s heart smote him after that he had numbered the people. And David said unto the Lord, I have sinned greatly in that I have done: and now, I beseech thee, O Lord, take away the iniquity of thy servant; for I have done very foolishly.

For when David was up in the morning, the word of the Lord came unto the prophet Gad, David’s seer, saying,

Go and say unto David, Thus saith the Lord, I offer thee three things; choose thee one of them, that I may do it unto thee.