This word is mentioned in the following aya: Quran 3: 28
[In this aya and some other ayat, God forbade the allying with disbelievers and idolaters (or associaters), and forbade loving them and exposing the secrets to them:]
{ 28. The believers should not take disbelievers for [their] allies a instead of believers b, and whoever does that will have nothing of God['s alliance] c; unless you are obliged to do this in order to avoid persecution d.
God bids you beware of Himself e; and f to God will be the final resort. g }
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a i.e. Believers should not take disbelievers as their allies to love and help them and expose the secrets of Muslims to them.
b i.e. they ally with them instead of allying with believers, but they should ally with the believers not with the disbelievers.
c i.e. anyone of you who allies with them, then God – be glorified – will not take care about him, but will quit him.
d i.e. if the power and authority is by their hands, and you are afraid lest you should be killed or persecuted; therefore, you pretend that you like them with your tongues not with your hearts; but it is not allowed to help them or expose the secrets of Muslims to them.
e Therefore, don't contradict His commands.
f following your death.
g So He will punish you for your allying with the disbelievers.