In the name of Allah most gracious most merciful,
Assalamualaikum wa rahmatuallahi wa barakatuhu,

Muslims dealing with kafir/non-muslims

16:125 Invite (all) to the way of thy Lord with wisdom and beautiful preaching; and argue with them in ways that are best and most gracious: for thy Lord knoweth best who have strayed from His Path and who receive guidance.

If Non-Muslims Do Not Accept Islam

109:1 Say: O ye that reject Faith!
2 I worship not that which ye worship
3 Nor will ye worship that which I worship.
4 And I will not worship that which ye have been wont to worship
5 Nor will ye worship that which I worship.
6 To you be your Way and to me mine.

2:256 Let there be no compulsion in religion. Truth stands out clear from error; whoever rejects evil and believes in Allah hath grasped the most trustworthy hand-hold that never breaks. And Allah heareth and knoweth all things.

There is no compulsion in religion ,so non-muslims can practice there religion but they must not have enemity with Muslims.Muslims can have treaties with them,they can be dhimmis .Muslims can take help from non-Muslims to fight against non-muslims but not with muslims,because believers are single brotherhood.

Taking Non-Muslims Friendship Only If There Death Threat from Them

3:28. Let not the believers take the disbelievers as Auliyâ (supporters, helpers, etc.) instead of the believers, and whoever does that will never be helped by Allâh in any way, except if you indeed fear a danger from them. And Allâh warns you against Himself (His Punishment), and to Allâh is the final return.

Commentary by Ibn Kathir on the above verse:

Allah prohibited His believing servants from becoming supporters of the disbelievers, or to take them as comrades with whom they develop friendships, rather than the believers. Allah warned against such behavior when He said,


وَمَن يَفْعَلْ ذَلِكَ فَلَيْسَ مِنَ اللَّهِ فِي شَىْءٍ
(And whoever does that, will never be helped by Allah in any way) meaning, whoever commits this act that Allah has prohibited, then Allah will discard him. Similarly, Allah said,
 

يأَيُّهَا الَّذِينَ ءَامَنُواْ لاَ تَتَّخِذُواْ عَدُوِّى وَعَدُوَّكُمْ أَوْلِيَآءَ تُلْقُونَ إِلَيْهِمْ بِالْمَوَدَّةِ
(O you who believe! Take not My enemies and your enemies as friends, showing affection towards them), until,


وَمَن يَفْعَلْهُ مِنكُمْ فَقَدْ ضَلَّ سَوَآءَ السَّبِيلِ
(And whosoever of you does that, then indeed he has gone astray from the straight path.) ﴿60:1﴾. Allah said,


يَـأَيُّهَا الَّذِينَ ءَامَنُواْ لاَ تَتَّخِذُواْ الْكَـفِرِينَ أَوْلِيَآءَ مِن دُونِ الْمُؤْمِنِينَ أَتُرِيدُونَ أَن تَجْعَلُواْ للَّهِ عَلَيْكُمْ سُلْطَاناً مُّبِيناً
(O you who believe! Take not for friends disbelievers instead of believers. Do you wish to offer Allah a manifest proof against yourselves) ﴿4:144﴾, and,


﴿يَـأَيُّهَا الَّذِينَ ءَامَنُواْ لاَ تَتَّخِذُواْ الْيَهُودَ وَالنَّصَـرَى أَوْلِيَآءَ بَعْضُهُمْ أَوْلِيَآءُ بَعْضٍ وَمَن يَتَوَلَّهُمْ مِّنكُمْ فَإِنَّهُ مِنْهُمْ
(O you who believe! Take not the Jews and the Christians as friends, they are but friends of each other. And whoever befriends them, then surely, he is one of them.) ﴿5:51﴾.

Allah said, after mentioning the fact that the faithful believers gave their support to the faithful believers among the Muhajirin, Ansar and Bedouins,


﴿وَالَّذينَ كَفَرُواْ بَعْضُهُمْ أَوْلِيَآءُ بَعْضٍ إِلاَّ تَفْعَلُوهُ تَكُنْ فِتْنَةٌ فِى الاٌّرْضِ وَفَسَادٌ كَبِيرٌ ﴾
(And those who disbelieve are allies of one another, (and) if you do not behave the same, there will be Fitnah and oppression on the earth, and a great mischief and corruption.) ﴿8:73﴾.


Allah said next,﴿إِلاَ أَن تَتَّقُواْ مِنْهُمْ تُقَـةً﴾

(unless you indeed fear a danger from them) meaning, except those believers who in some areas or times fear for their safety from the disbelievers. In this case, such believers are allowed to show friendship to the disbelievers outwardly, but never inwardly. For instance, Al-Bukhari recorded that Abu Ad-Darda' said, "We smile in the face of some people although our hearts curse them.'' Al-Bukhari said that Al-Hasan said, "The Tuqyah is allowed until the Day of Resurrection.'' Allah said,


﴿وَيُحَذِّرُكُمُ اللَّهُ نَفْسَهُ﴾
(And Allah warns you against Himself.) meaning, He warns you against His anger and the severe torment He prepared for those who give their support to His enemies, and those who have enmity with His friends,


﴿وَإِلَى اللَّهِ الْمَصِيرُ﴾

Allah says:18:102 Do the Unbelievers think that they can take my servants as protectors besides Me? Verily We have prepared Hell for the Unbelievers for (their) entertainment.

Deal Kindly & Justly With Them Who Are Really Good

60:8 Allah forbids you not with regard to those who fight you not for (your) Faith nor drive you out of your homes from dealing kindly and justly with them: for Allah loveth those who are just.
9 Allah only forbids you with regard to those who fight you for (your) Faith and drive you out of your homes and support (others) in driving you out from turning to them (for friendship and protection). It is such as turn to them (in these circumstances) that do wrong.
 

Real Friends Of Muslims

5:55 Your (real) friends are (no less than) Allah His Apostle and the (fellowship of) believers those who establish regular prayers and regular charity and they bow down humbly (in worship).
56 As to those who turn (for friendship) to Allah His Apostle and the (fellowship of) believers it is the fellowship of Allah that must certainly triumph.

Allah Knows Best