Midrasch zu Divrej Hajamim I 21:14

Rabbi Abbahu said: Know thou the power of repentance. Come and see from David, king of Israel. For the Holy One, blessed be He, had sworn to the forefathers that He would multiply their seed like the stars of the heavens. And David came to count their number. The Holy One, blessed be He, said to him: David ! I have sworn to the forefathers that I would multiply their seed as the stars of the heavens. And thou comest to annul My word. For thy sake the flock is given over to destruction; and in three hours there fell seventy thousand men, as it is said, "And there fell of Israel seventy thousand men" (1 Chron. 21:14). Rabbi Simeon said: Only Abishai, son of Zeruiah, fell amongst the Israelites, for he was equal in his good deeds and his knowledge of the Torah to the seventy thousand men, as it is said, "And there fell of Israel seventy thousand men" (ibid.). "Men" is not written here, only "man." And David heard and rent his garments, and clothed himself in sackcloth and ashes, and he fell upon his face to the ground before the ark of the covenant of God.