Exodus 32:28-30

Young's Literal Translation

²⁸ And the sons of Levi do according to the word of Moses, and there fall of the people on that day about three thousand men,

²⁹ and Moses saith, `Consecrate your hand to-day to Jehovah, for a man [is] against his son, and against his brother, so as to bring on you to-day a blessing.'

³⁰ And it cometh to pass, on the morrow, that Moses saith unto the people, `Ye -- ye have sinned a great sin, and now I go up unto Jehovah, if so be I atone for your sin.'