Question

What exactly are good deeds (as-salihat)? I know some but maybe not all of them.

Answer

Praise be to Allah.

Good deeds are those which are in accordance with sharee’ah, and which are done sincerely for the sake of Allaah. Shaykh al-Islam [Ibn Taymiyah] defined ‘ibaadah (worship) as “a general term which includes all that Allaah loves and is pleased with, be it words or deeds, both inward and outward; these are of many kinds and we cannot list them, let alone enumerate them, but we will mention some of them: 

1.Belief in Allaah – which includes belief in Allaah, His angels, His Books, His Messengers, the Last Day, and the divine will and decree (al-qadar), both good and bad.

2.Prayer done on time – there are five prayers that Allaah has enjoined during the night and day. The Sahaabah (may Allaah be pleased with hem) were all agreed that the one who does not pray is a kaafir. It is not permissible to delay the prayers beyond their appointed time. It is obligatory to perform all the obligatory parts of the prayer, and the Muslim should pray as the Prophet (peace and blessings of Allaah be upon him) prayed.

3.Acceptable Hajj – which means:

a.It should be done with halaal money (earned from permissible sources)

b.One should avoid immoral actions, sin and arguments whilst doing Hajj

c.He should perform all the rituals according to the Sunnah of the Prophet (peace and blessings of Allaah be upon him).

d.He should not do Hajj to show off, rather he should do it sincerely for the sake of Allaah.

e.He should not follow it with any act of disobedience or sin.

4.Honouring one’s parents – which means obeying them in acts of obedience towards Allaah; it is not permissible to obey them in matters of disobedience or sin. Honouring them also means not raising one’s voice to them, and not offending them with hurtful words. It also includes spending on them, and serving them.

5.Jihad for the sake of Allaah. Allaah has prescribed jihad in order to establish Tawheed and spread Islam throughout the world. Allaah has prepared a great reward for the mujaahideen.

6.Loving for the sake of Allaah and hating for the sake of Allaah. This means that the Muslim loves his fellow Muslim for the sake of Allaah, not for his colour, nationality or wealth, rather for his obedience to his Lord and his closeness to Him. Similarly he hates the sinner for his disobedience towards Allaah.

7.Reading and reciting Qur’aan – whether that is in the portion he reads each day or what he recites in prayers at night (qiyaam al-layl).

8.Persisting in acts of worship even if they are little. The Prophet (peace and blessings of Allaah be upon him) loved actions that were done consistently, even if they were little. A small action done persistently is better than a greater action done intermittently.

9.Fulfilling one’s trusts. This is an obligatory action and is one of the greatest of deeds. It is known in Islam that the hypocrite is the one who betrays his trust and does not render trusts back to the people who entrusted them to him.

10. Being forgiving towards people. This means foregoing one’s personal rights, forgiving the one who has done you wrong, if doing so will lead to his changing, or if he has repented and regrets what he did. The Prophet (peace and blessings of Allaah be upon him) said: “A person only increases in honour by forgiving.” Narrated by Muslim, 2588

11. Being truthful in speech. The Prophet (peace and blessings of Allaah be upon him) said: “A man will keep on speaking the truth and endeavouring to tell the truth until he will be recorded with Allaah as a speaker of truth. Truthfulness is a means of salvation; it is a great characteristic which was one of the features of the Prophets and those who followed them in truth.” Narrated by Muslim, 2607.

12. Spending for the sake of Allaah. This includes spending on jihad, and spending on one’s parents, the poor and needy, on building mosques, on printing copies of the Qur’aan and Islamic books, and spending on one’s family and children.

13. Ensuring that the Muslims are safe from one’s words and actions. That means refraining from gossip, backbiting, slander, insults and curses, and refraining from hitting or beating those who do not deserve such treatment.

14. Feeding the hungry – which includes feeding both humans and animals.

15. Spreading the greeting of salaam to those whom you know and those whom you do not know – except in the case of those whom the texts say we should not initiate the greeting of salaam with, namely the kuffaar.

16. Helping the needy, wayfarers and those who are helpless.

17. Keeping your evil away from people, which is an act of charity that may benefit you.

And there are many other good deeds. 

The following hadeeth enumerates several good deeds: 

Al-Bayhaqi narrated that Abu Dharr said: I said, “O Messenger of Allaah, what will save a person from Hellfire?”

 He said, “Belief in Allaah.” 

I said, “O Messenger of Allaah, are there are any deeds that should accompany that belief?” 

He said, ‘He should give from that provision which Allaah has granted him.” 

I said, “O Messenger of Allaah, what if he is poor and does not have anything to give?” 

He said, “He should enjoin what is good and forbid what is evil.” 

I said, “O Messenger of Allaah, what if he cannot enjoin what is good and forbid what is evil?” 

He said, “He should help the one who is helpless (i.e., has no skills and cannot earn a learning).” 

I said, “What if he himself is helpless and cannot do anything?” 

He said, “He should help one who has been wronged.” 

I said, “What if he is weak and cannot help one who has been wronged?”  

He said, “You do not want to think of your companion as having any good in him. Let him refrain from harming people.” 

I said, “O Messenger of Allaah, if he does that, will he enter Paradise?” 

He said, “There is no believer who does not strive to acquire one of these characteristics, but I will take him by the hand and lead him into Paradise.”  

Classed as saheeh by al-Albaani in al-Targheeb, 876 

And Allaah is the Source of strength.

Source: https://islamqa.info/en/answers/26242/good-deeds

Even just a smile is a charitable act and good deed.