Ta-Ha - 20:87
We did not break our promise to you according to our own minds. The ornaments of that people were carried to us. We threw them away. This is what Samiri has brought forth.
Our Lord had taken a promise from the Children of Israel through Prophet Moses that they would serve Him alone:
The Cow/2:83
We took a promise from the Children of Israel: You shall serve none but Allah, and you shall do good to parents and relatives and orphans and the poor. You shall speak to people in friendship. You will observe the prayer and pay the zakat. But after that you turned away, except a few of you.