From the works of Ibn Rajab al-Hanbali, Ibn al-Qayyim al-Jawziyya, and Imam Ghazali
"And keep yourself (O Muhammad!) patiently with those who call on their Lord (your companions who remember their Lord with glorification, praising in prayers, etc., and other righteous deeds, etc.) morning and afternoon, seeking His Face, and let not your eyes overlook them, desiring the pomp and glitter the life of the world; and obey not him whose heart We have made heedless of Our Remembrance, one who follows his own lusts and whose affair (deeds) has been lost." The Holy Quran: 18:28.
1. Unnecessary Talking
In a hadith related on the authority of Mu'adh, the Prophet (s) said, "Shall I not tell you how to control all that?" I said, "Yes do, O Messenger of Allah." So he held his tongue between his fingers, and then he said: "Restrain this." I said, "Oh Prophet of Allah, are we accountable for what we say?" He (s) said, "May your mother be bereft by your loss! Is there anything more than the harvest of the tongues that throws people on their faces (or he said 'on their noses') into the Fire?"
What is meant here by 'the harvest of the tongues' is the punishment for saying forbidden things. A man, through his actions and words, sows the seeds of either good or evil. On the Day of Resurrection he harvests their fruits. Those who sow the seeds of good words and deeds harvest honour and blessings; those who sow the seeds of evil words and deeds reap only regret and remorse.
A hadith related by Abu Huraira says:
"What mostly causes people to be sent to the Fire are the two openings: the mouth and the private parts."
2. Unrestrained Glances
Staring and gazing without restraint is disobedience to Allah:
"Tell the believing men to lower their gaze and guard their modesty; that is more purifying for them. Surely Allah is aware of what they do. (24:30)
3. Too Much Food
Al-Miqdam ibn Ma'd Yakrib said:
I heard the Messenger of Allah (s) say: "The son of Adam fills no vessel more displeasing to Allah than his stomach. A few morsels should be enough for him to preserve his strength. If he must fill it, then he should allow a third for his food, a third for his drink and leave a third empty for easy breathing."
4. Keeping Bad Company
A servant should benefit from companionship. In order to do so he should divide people into four categories, and be careful not to get them mixed up, for once one of them is mixed with another, then evil can find its way through to him:
The first category are those people whose company is like food: it is indispensable, night or day. Once a servant has taken his need from it, he leaves it be until he requires it again, and so on. These are the people with knowledge of Allah-of His commands, of the scheming of His enemies, and of the diseases of the heart and their remedies- who wish well for Allah, His Prophet (s) and His servants. Associating with this type of person is an achievement in itself.
The second category are those people whose company is like a medicine. They are only required when a disease sets in. When you are healthy, you have no need of them. However, mixing with them is sometimes necessary for your livelihood, businesses, consultation and the like. Once what you need from them has been fulfilled, mixing with them should be avoided.
The third category are those people whose company is harmful. Mixing with this type of person is like a disease, in all its variety and degrees and strengths and weaknesses. Associating with one or some of them is like an incurable chronic disease. You will never profit either in this life or in the next life if you have them for company, and you will surely lose either one or both of your religion and your livelihood because of them. If their companionship has taken hold of you and is established, then it becomes a fatal, terrifying sickness.
Amongst such people are those who neither speak any good that might benefit you, nor listen closely to you so that they might benefit from you. They do not know their souls and consequently put their selves in their rightful place. If they speak, their words fall on their listeners' hearts like the lashes of a cane, while all the while they are full of admiration for and delight in their own words.
They cause distress to those in their company, while believing that they are the sweet scent of the gathering. If they are silent, they are heavier than a massive millstone-too heavy to carry or even drag across the floor.18
All in all, mixing with anyone who is bad for the soul will not last, even if it is unavoidable. It can be one of the most distressing aspects of a servant's life that he is plagued by such person, with whom it may be necessary to associate. In such a relationship, a servant should cling to good behavior, only presenting him with his outward appearance, while disguising his inner soul, until Allah offers him a way out of his affliction and the means of escape from this situation.
The fourth category are those people whose company is doom itself. It is like taking poison: its victim either finds an antidote or perishes. Many people belong to this category. They are the people of religious innovation and misguidance, those who abandon the Sunnah of the Messenger of Allah (saws) and advocate other beliefs. They call what is the Sunnah a bid'a and vice-versa. A man with any intellect should not sit in their assemblies nor mix with them. The result of doing so will either be the death of his heart or, at the very best, its falling seriously ill.