This Bible contradiction is from the Skeptic's Annotated Bible.

Verses

For offering a burnt offering.

1 Samuel 13:9 View context

And Saul said, Bring hither a burnt offering to me, and peace offerings. And he offered the burnt offering.

For incomplete genocide.

1 Samuel 15:2-3 View context

Thus saith the LORD of hosts, I remember [that] which Amalek did to Israel, how he laid [wait] for him in the way, when he came up from Egypt.

Now go and smite Amalek, and utterly destroy all that they have, and spare them not; but slay both man and woman, infant and suckling, ox and sheep, camel and ass.