The Criterion Between The Allies of the Merciful & the Allies of the Devil by Imam Ibn Taymiyyah

We testify that there is no deity except Allah, alone and with no partner. And, we testify that Muhammad is His slave and messenger. He sent him with the guidance and the way of truth so that He (i.e. Allah) might make it predominate over all other ways, and Allah is sufficient as a witness. He sent him preceding the Hour (qiyama), as a bringer of good tidings, a warner, and a caller to Allah by His permission, and as a beacon light. He (Allah) guided with it those who had been lost, and gave sight to those who had been blind, gave uprightness and order to those who had been following unbridled impulse; He opened unseeing eyes, deaf ears, and sealed hearts. With it, He established the criterion for distinguishing truth from falsehood, guidance from going astray, uprightness from following of whims, the believers from the disbelievers, the joyous people of paradise and the miserable people of the fire, and the allies of Allah from His enemies.
Whoever the Prophet (sas) has attested to as being among the allies of Allah, are the awliyaa’ (friends or allies) of the Merciful, and whoever the Prophet has described as being among the enemies of Allah, are indeed among the enemies of Allah, and are among the awliyaa’ of the shaitaan (devil). Allah has explained in His Book, and in the Sunnah of His Prophet that He has awliyaa’ among the people and that shaitaan also has his awliyaa’, and He has differentiated between these two types of awliyaa’.
Allah said: [Indeed, there is no fear upon the awliyaa’ of Allah, nor shall they grieve, those who believe and are ever pious in their actions. To them are glad tidings in this life and in the hereafter. There is no changing the words of Allah. That, then, is the great success.] Qur’an 10/62-64 [Allah is the protector (ally) of those who believe, He takes them out of the darkness into the light. As for the disbelievers, their allies are the taaghoot who take them out of the light and into the darkness. Those are the people of the fire, and they will be in it forever.] Qur’an 2/257 [O, you who believe, do not take the Jews and the Christians as allies. They are allies of each other. Whoever among you puts his allegiance with them, is certainly one of them. Allah does not guide a people who oppress. And so, you see those in whose heart is sickness rushing to (make alliances with) them, saying: “We fear being caught in some unfortunate turn of events”.