Genesis 6:6
5 But the Lord saw that the wickedness of humankind had become great on the earth. Every inclination of the thoughts of their minds was only evil all the time. 6 The Lord regretted that he had made humankind on the earth, and he was highly offended. 7 So the Lord said, “I will wipe humankind, whom I have created, from the face of the earth—everything from humankind to animals, including creatures that move on the ground and birds of the air, for I regret that I have made them.”
1 Samuel 15:35
33 Samuel said, “Just as your sword left women childless, so your mother will be the most bereaved among women.” Then Samuel hacked Agag to pieces there in Gilgal before the Lord. 34 Then Samuel went to Ramah, while Saul went up to his home in Gibeah of Saul. 35 Until the day he died, Samuel did not see Saul again. Samuel did, however, mourn for Saul, but the Lord regretted that he had made Saul king over Israel.
Notes and References
"... We pursue the topic of divine repentance more generally at chapter 26, but note here the unusual theme that God will change his mind with respect to a promised good. This kind of divine action is rare in the Old Testament, having links to two other texts. At the outset of the flood story God repents of having made the good creation (Genesis 6:5) and at the beginning of the monarchy God repents of having made Saul king (1 Samuel 15:35). At the same time, these two instances are unusual in that God turns around and offers unconditional promises, both to the creation as a whole (see Genesis 8:21-22; 9:8-17) and to the Davidic line (1 Samuel 15:28-29; 2 Samuel 7). In the Jeremiah text a promised “good” is also opened up to the possibility of divine repentance. Rather varied promised “goods” seem to be in view (compare Jeremiah 12:15-17; 27:1-11) ..."
Fretheim, Terence E. The Smyth & Helwys Bible Commentary: Jeremiah (p. 272) Smith & Helwys, 2002