This reading is from the special Torah portion read on the Shabbat during the festival of Sukkot. The complete reading for the intermediate Shabbat is Exodus 33:12-34:26.
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!"