Al-Jalees (singular of al-julasaa) literally means the one you "sit" with, i.e., whose company you keep. It is very important for a Muslim to be careful about those to whom he gives his companionship and friendship. This is because friendship and companionship leads to allegiance and loyalty and that can only be directed to the Muslims. Allah said:
لَا يَتَّخِذِ الْمُؤْمِنُونَ الْكَافِرِينَ أَوْلِيَاءَ مِنْ دُونِ الْمُؤْمِنِينَ وَمَنْ يَفْعَلْ ذَلِكَ فَلَيْسَ مِنَ اللَّهِ فِي شَيْءٍ إِلَّا أَنْ تَتَّقُوا مِنْهُمْ تُقَاةً وَيُحَذِّرُكُمُ اللَّهُ نَفْسَهُ وَإِلَى اللَّهِ الْمَصِيرُ
{Believers are not to take disbelievers as awilyaa and not the believers. Allah has nothing to do with those who do so unless it is merely done to protect yourselves from them. Allah warns you about Himself. To Allah is your final state.} Aal 'Imraan: 28
Ash-Shaukaani said about the meaning of "taking the disbelievers as awliyaa": "They like them, are kind to them and are inclined toward them with their hearts and to helping and supporting them." Then, he explains Allah's statement that "Allah has nothing to do with those who do so", saying: "He has drifted away from Allah in every way and Allah has declared his non-relation to him."
Companions can be divided into two categories:
Righteous friend: A fellow Muslim and a person of upright character and practice. This is the one with whom you can feel comfortable that you have chosen a companion in a way pleasing to Allah Most High.
Evil friend: This is a companion of evil nature and bad character. Disbelief is the worst possible bad character, even if their friendship seems wholesome on other levels. They cannot help you, you will regret being in their presence on Qiyama and you will be avowed enemies after the resurrection.
Friendship is a precious thing not to be given lightly. Friend has been called "sadeeq" in Arabic from the word for truthfulness and honesty - friends should not deceive, trick or betray each other. It has also been called "khaleel" from the word for sections because the love for a true friend fills every section and part of the heart. True friendship of a Muslim is only allowed to another Muslim and preferably one of good character and practice.
Before you cultivate your friendships and your relationships think to your self: 1) Is this the one whom Allah would love for me to direct my friendship and energy? and 2) I Qiyama came at this moment, is this the one with whom I would like to stand before Allah in his company? If you choose your friends from other than the people of belief and taqwa, they will be your enemies on Qiyama. Allah said:
الْأَخِلَّاءُ يَوْمَئِذٍ بَعْضُهُمْ لِبَعْضٍ عَدُوٌّ إِلَّا الْمُتَّقِينَ (67) يَا عِبَادِي لَا خَوْفٌ عَلَيْكُمُ الْيَوْمَ وَلَا أَنْتُمْ تَحْزَنُونَ (68)
{The dearest of friends will be enemies to one another on that day except for the people of taqwa} Az-Zukhruf: 67
Ash-Shaukaani said about this verse: "The meaning is that the dear friends who loved one another in this life will become enemies to one another when the Hour reaches them. They will find that those things which brought them together as friends are now reasons for their punishment and so they become enemies. Allah says: "except for the people of taqwa" for they will enjoy their friendship in this life and in the hereafter."
In Sura Az-Zukhruf, Allah speaks about the people of Paradise after they have found all of the delights which are theirs, saying:
قَالَ قَائِلٌ مِنْهُمْ إِنِّي كَانَ لِي قَرِينٌ (51) يَقُولُ أَئِنَّكَ لَمِنَ الْمُصَدِّقِينَ (52) أَئِذَا مِتْنَا وَكُنَّا تُرَابًا وَعِظَامًا أَئِنَّا لَمَدِينُونَ (53) قَالَ هَلْ أَنْتُمْ مُطَّلِعُونَ (54) فَاطَّلَعَ فَرَآهُ فِي سَوَاءِ الْجَحِيمِ (55) قَالَ تَاللَّهِ إِنْ كِدْتَ لَتُرْدِينِ (56) وَلَوْلَا نِعْمَةُ رَبِّي لَكُنْتُ مِنَ الْمُحْضَرِينَ (57)
{Then they came close to one another, asking each other (50) One of them said: I used to have a companion (51) who used to say: "Are you among those who believe this?" (52) that when we have died and turned into dust and bones that we will be held responsible? (53) He said: "Are you looking?" (54) So they looked and they saw him in the bottom of the fire. (55) He said: "By Allah! You very nearly dragged me down. (56) If it were not for the favor of my Lord I would have been among those brought (to the fire)} As-Saafaat: 51-57
You will surely be affected by those whose company you keep in this life and in the hereafter. If you think otherwise then you are in a state of denial and self-deception. In this country, we should always maintain cordial and kind relations with the disbelievers for the purpose of showing them a good example of Islam and for making da'wah. We must never, however, cross that line into true friendship. Friendship with Allah's enemies will lead to allegiance and loyalty to them which will put us far from Allah and He will declare his non-relation to us! Even before that stage, many forms of harm can come to use because of this association.
The Prophet (sas) said: "The righteous companion is like the seller of Musk: even if you don't actually get some musk, its pleasant scent reaches you. The evil companion is like the man working the bellows: even if it doesn't burn your clothing, you are afflicted with its smoke." Muslim & Bukhari in its meaning, this from Abu Daud & An-Nasaa'i
The Prophet (sas) said: "Do not take any companion except a believer and let only the pious eat your food." Abu Daud & At-Tirmidhi.
The Prophet (sas) said: "Every man is on the religion of his dear friend, so be very careful to whom you direct your close friendship."