This reading is from the special Torah portion read on the Shabbat during Passover, Parshat Pesach, Exodus 33:12-34:26. The reading for the first day of Passover is Exodus 12:21-51.
So Moses carved two tablets of stone, like the first, and early in the morning he went up on Mount Sinai, as the Lord had commanded him, taking the two stone tablets with him. The Lord came down in a cloud; He stood with him there, and proclaimed the name Lord. The Lord passed before him and proclaimed: "The Lord! the Lord! a God compassionate and gracious, slow to anger, abounding in kindness and faithfulness, extending kindness to the thousandth generation, forgiving iniquity, transgression, and sin; yet He does not remit all punishment, but visits the iniquity of parents upon children and children's children, upon the third and fourth generations." Moses hastened to bow low to the ground in homage, and said, "If I have gained Your favor, O Lord, pray, let the Lord go in our midst, even though this is a stiffnecked people. Pardon our iniquity and our sin, and take us for Your own!"
He said: I hereby make a covenant. Before all your people I will work such wonders as have not been wrought on all the earth or in any nation; and all the people who are with you shall see how awesome are the Lord's deeds which I will perform for you.