Bowing To Idols

Ibn Taymiyyah:

And likewise belying the Messenger (saw) in heart and hating him and envying him and abiding from following him are bigger sins than doing apparent/public deeds that are empty of the afore-mentioned, like murder, fornication, drinking and robbery, and what is Kufr from among the apparent deeds and actions are: prostration to idols, and insulting the Messenger (saw) and things like that, because these actions necessitate Kufr in one's heart, other than that if someone prostrates to an idol and does not intend prostration to that idol in his heart and in his heart he intends to prostrate for Allah (swt), this won't be Kufr, and this is indeed permissible if the person lives among the polytheists and fears them for his life, so he aligns with them in the apparent actions, but intends in his heart the prostration for Allah (swt). As some of the Muslim scholars and scholars of Ahl Al-Kitab have done like this with a group of polytheists in order to invite them to Islam, so they have embraced Islam in his hands, because he did not invoke their hatred in the beginning. 

Source: Majmu' Al-Fatawa. Vol. 14, Pg. # 120.