As long as Rasulullah (sallallahu ‘alaihi wasallam) sufficed on inviting the people to Islam, the Quraish did not interfere with him. However, when he began to invite to Islam openly, began to speak ill of the idol worshippers and began to prevent people from engaging in kufr and shirk, the Quraish began to show him enmity and oppose him. However, Abu Taalib continued to support and assist Rasulullah (sallallahu ‘alaihi wasallam).
On one occasion, a delegation of the Quraish came to Abu Taalib and said, “Your nephew speaks ill of our idols, criticizes our religion, shows us to be fools and says that our forefathers were misguided. You should either prevent him from doing this or stop intervening between us so that we can sort out the matter with him.” Abu Taalib gently and tactfully sidestepped and brushed off the issue while Rasulullah (sallallahu ‘alaihi wasallam) continued inviting towards the oneness of Allah Ta‘ala and speaking against kufr and shirk.
The fire of hatred and enmity of Abu Lahab and his friends flared up even more. They sent another delegation to Abu Taalib saying, “We accept and acknowledge your nobility and high status among us, but we will never tolerate our idols being criticized and our forefathers being referred to as fools. Either stop your nephew or we will fight and oppose him until one of us will perish.” Saying this, they departed.
(Seeratul Mustafa 1/174-175)