3:118
يَٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوا۟ لَا تَتَّخِذُوا۟ بِطَانَةًۭ مِّن دُونِكُمْ لَا يَأْلُونَكُمْ خَبَالًۭا وَدُّوا۟ مَا عَنِتُّمْ قَدْ بَدَتِ ٱلْبَغْضَآءُ مِنْ أَفْوَٰهِهِمْ وَمَا تُخْفِى صُدُورُهُمْ أَكْبَرُ ۚ قَدْ بَيَّنَّا لَكُمُ ٱلْءَايَٰتِ ۖ إِن كُنتُمْ تَعْقِلُونَ
O you who have believed, do not take as intimates those other than yourselves, for they will not spare you [any] ruin. They wish you would have hardship. Hatred has already appeared from their mouths, and what their breasts conceal is greater. We have certainly made clear to you the signs, if you will use reason.
Translation · Saheeh International
Tafsir
Ibn Kathīr (abridged)
Prohibition of Taking Allies From Disbelievers Who Ridicule Islam
Allah forbids His believing servants from taking the hypocrites as allies, so that the hypocrites do not have the opportunity to expose the secrets of the believers and their plans against their enemies. The hypocrites try their very best to confuse, oppose and harm the believers any way they can, and by using any wicked, evil means at their disposal. They wish the very worst and difficult conditions for the believers. Allah said,
لاَ تَتَّخِذُواْ بِطَانَةً مِّن دُونِكُمْ
(Take not as (your) Bitanah those other than your own) 3:118, in reference to taking followers of other religions as consultants and allies, for advisors of a certain person have access to his most secret affairs. Al-Bukhari and An-Nasa'i recorded that, Abu Sa`id said that the Messenger of Allah ﷺ said,
«مَا بَعَثَ اللهُ مِنْ نَبِيَ وَلَا اسْتَخْلَفَ مِنْ خَلِيفَةٍ إِلَّا كَانَتْ لَهُ بِطَانَتَانِ: بِطَانَةٌ تَأْمُرُهُ بِالْخَيْرِ وَتَحُضُّهُ عَلَيْهِ، وَبِطَانَةٌ تَأْمُرُهُ بِالسُّوءِ وَتَحُضُّهُ عَلَيْهِ، وَالْمَعْصُومُ مَنْ عَصَمَ الله»
(Allah has not sent any Prophet nor was there any Khalifah but they have two types of allies, one that commands him with righteousness and advises it, and another that commands him with evil and advises him with it. Only those whom Allah gives immunity are immune.)