Where does the Bible say that God’s patience is long but not endless?

Answer:

"And the LORD passed before him and proclaimed, "The LORD, the LORD God, merciful and gracious, longsuffering, and abounding in goodness and truth, keeping mercy for thousands, forgiving iniquity and transgression and sin, by no means clearing the guilty, visiting the iniquity of the fathers upon the children and the children's children to the third and the fourth generation"" (Exodus 34:6-7).

"The LORD is slow to anger and great in power, And will not at all acquit the wicked. The LORD has His way In the whirlwind and in the storm, And the clouds are the dust of His feet" (Nahum 3).

"The LORD is merciful and gracious, slow to anger, and abounding in mercy. He will not always strive with us, nor will He keep His anger forever. He has not dealt with us according to our sins, nor punished us according to our iniquities. For as the heavens are high above the earth, so great is His mercy toward those who fear Him; as far as the east is from the west, so far has He removed our transgressions from us" (Psalms 103:8-12).

"Or do you despise the riches of His goodness, forbearance, and longsuffering, not knowing that the goodness of God leads you to repentance? But in accordance with your hardness and your impenitent heart you are treasuring up for yourself wrath in the day of wrath and revelation of the righteous judgment of God, who "will render to each one according to his deeds"" (Romans 2:4-6).