If he promised to help, he will not go back on his promise.

如果他答应帮忙，他就不会食言。

《新英汉大辞典》

I can not go back on what I said.

我不能背约我所说的话。

youdao

This is a demand we will not go back on.

这是我们不会放弃的要求。

youdao

The Palestinians insist they will not go back to negotiations until Israel freezes all construction on Jewish settlements in the occupied West Bank.

VOA: standard.2009.10.30

But the government could not now go back on its promises, he said.

BBC: 'Keep the faith' on Post Office

Mick Keane, of Dartford, Kent, has been told not to go back on health grounds, but he continues to protest his innocence.

BBC: Plane-spotters' notes under scrutiny

Quakers and Catholics sided with the king, and so did many settlers of German and Dutch origin, as well as most Scots Highlanders, who had sworn an oath of loyalty to the Hanoverian crown in defeat and were not about to go back on it.

ECONOMIST: America's revolution: The king's shilling | The