What do Muslims believe to be evil?

Answer 1

Muslims believe that it is evil all what is against Qur'an instructions and against the teachings of prophet Muhammad (peace be upon him). Examples of evil are:

• Violating the Islam five pillars (refer to related question below)
• worshiping a partner to Allah (or God and same God worshiped in Christianity and Judaism).
• killing innocent man, or woman, or boy, or a child
• committing fornication (practicing sex outside licit marriage)
• ill treatment to parents and neighbors
• robbery
• cheating
• not saying the truth and saying lies.
• practicing same sex or having same sex marriage
• not taking care of orphans and putting hands on their wealth and properties
• feeling false pride over people
• not helping the poor and needy people
• spying on people and mentioning them with bad words and accusing them falsely

  peaking loudly and with rude words

• not keeping promise
• ....

Quran says:

{Say (O Muhammad SAW): "Come, I will recite what your Lord has prohibited you from: Join not anything in worship with Him; be good and dutiful to your parents; kill not your children because of poverty - We provide sustenance for you and for them; come not near to Al-Fawahish (shameful sins, illegal sexual intercourse, etc.) whether committed openly or secretly, and kill not anyone whom Allah has forbidden, except for a just cause . This He has commanded you that you may understand. And come not near to the orphan's property, except to improve it, until he (or she) attains the age of full strength; and give full measure and full weight with justice. We burden not any person, but that which he can bear. And whenever you give your word (i.e. judge between men or give evidence, etc.), say the truth even if a near relative is concerned, and fulfill the Covenant of Allah, This He commands you, that you may remember. (152) "And verily, this is my Straight Path, so follow it, and follow not (other) paths, for they will separate you away from His Path. This He has ordained for you that you may become Al-Muttaqun } (17:151-153)

Qur'an says also:

{ Set not up with Allah any other ilah (god), (O man)! (This verse is addressed to Prophet Muhammad SAW, but its implication is general to all mankind), or you will sit down reproved, forsaken (in the Hell-fire). (22) And your Lord has decreed that you worship none but Him. And that you be dutiful to your parents. If one of them or both of them attain old age in your life, say not to them a word of disrespect, nor shout at them but address them in terms of honour. (23) And lower unto them the wing of submission and humility through mercy, and say: "My Lord! Bestow on them Your Mercy as they did bring me up when I was small." (24) Your Lord knows best what is in your inner-selves. If you are righteous, then, verily, He is Ever Most Forgiving to those who turn unto Him again and again in obedience, and in repentance. (25) And give to the kindred his due and to the Miskin (poor) and to the wayfarer. But spend not wastefully (your wealth) in the manner of a spendthrift. [Tafsir. At-Tabari, Vol. 10, Page 158 (Verse 9:60)]. (26) Verily, spendthrifts are brothers of the Shayatin (devils), and the Shaitan (Devil - Satan) is ever ungrateful to his Lord. (27) And if you (O Muhammad SAW) turn away from them (kindred, poor, wayfarer, etc. whom We have ordered you to give their rights, but if you have no money at the time they ask you for it) and you are awaiting a mercy from your Lord for which you hope, then, speak unto them a soft kind word (i.e. Allah will give me and I shall give you). (28) And let not your hand be tied (like a miser) to your neck, nor stretch it forth to its utmost reach (like a spendthrift), so that you become blameworthy and in severe poverty. (29) Truly, your Lord enlarges the provision for whom He wills and straitens (for whom He wills). Verily, He is Ever All-Knower, All-Seer of His slaves. (30) And kill not your children for fear of poverty. We provide for them and for you. Surely, the killing of them is a great sin. (31) And come not near to the unlawful sexual intercourse. Verily, it is a Fahishah [i.e. anything that transgresses its limits (a great sin)], and an evil way (that leads one to Hell unless Allah forgives him). (32) And do not kill anyone which Allah has forbidden, except for a just cause. And whoever is killed (intentionally with hostility and oppression and not by mistake), We have given his heir the authority [(to demand Qisas, Law of Equality in punishment or to forgive, or to take Diya (blood money)]. But let him not exceed limits in the matter of taking life (i.e. he should not kill except the killer only). Verily, he is helped (by the Islamic law). (33) And come not near to the orphan's property except to improve it, until he attains the age of full strength. And fulfil (every) covenant. Verily! the covenant, will be questioned about. (34) And give full measure when you measure, and weigh with a balance that is straight. That is good (advantageous) and better in the end. (35) And follow not (O man i.e., say not, or do not or witness not, etc.) that of which you have no knowledge (e.g. one's saying: "I have seen," while in fact he has not seen, or "I have heard," while he has not heard). Verily! The hearing, and the sight, and the heart, of each of those you will be questioned (by Allah). (36) And walk not on the earth with conceit and arrogance. Verily, you can neither rend nor penetrate the earth, nor can you attain a stature like the mountains in height. (37) All the bad aspects of these (the above mentioned things) are hateful to your Lord. (38)}.(17:22-38)

For good morals as extracted from Quran refer to related question below.