Praise be to Allah.
It is very important to know that every righteous deed that a person does may be part of that with which Allah will cause the balance of his good deeds to weigh heavily on the Day of Resurrection. Allah, may He be exalted, says (interpretation of the meaning):
“Indeed, Allah does not do injustice, [even] as much as an atom's weight; while if there is a good deed, He multiplies it and gives from Himself a great reward”
“So whoever does an atom's weight of good will see it,
And whoever does an atom's weight of evil will see it”
But there are texts which speak of specific deeds which will weigh particularly heavy in the doer’s balance on the Day of Resurrection. These include the following:
1. Tahleel, or saying Laa ilaaha ill-Allah (there is no god but Allah). This is the deed that will weigh most heavily in the balance.
It was narrated that ‘Abdullah ibn ‘Amr ibn al-‘Aas said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “Allah will bring forth a man belonging to my ummah before all creatures and will spread ninety-nine scrolls [containing the record of his bad deeds] for him, each scroll extending as far as the eye can see. Then He will say, ‘Do you object to anything in this? Have my scribes who keep note wronged you?’ He will say, ‘No, my Lord.’ He will ask him, ‘Do you have any excuse?’ He will say, ‘No my Lord.’ Allah will say, ‘On the contrary, you have with Us a good deed, and you will not be wronged this Day.’ A slip of paper will then be brought out, on which are the words ‘Ashhadu an laa ilaaha ill-Allah wa ashhadu anna Muhammadan ‘abduhu wa rasooluhu (I bear witness that there is no god but Allah, and I bear witness that Muhammad is His slave and His Messenger).’ Allah will say, ‘Bring your balance.’ The man will say, ‘O Lord, what is this slip of paper in comparison to these scrolls?’ And He will reply, ‘You will not be wronged.’ The scrolls will then be put in one side of the Balance and the slip of paper in the other, and the scrolls will become light and the slip of paper heavy, for nothing could compare in weight to the name of Allah.”
Narrated by Ahmad (6699) and at-Tirmidhi (2639); classed as saheeh by Shaykh al-Albaani (may Allah have mercy on him).
2. Remembrance of Allah, may He be exalted: tasbeeh, tahmeed, tahleel and takbeer
It was narrated from Abu Hurayrah (may Allah be pleased with him) that the Prophet (blessings and peace of Allah be upon him) said: “Two words which are light on the tongue but will weigh heavily in the Balance and are beloved to the Most Merciful: Subhaan Allah il-‘Azeem, Subhaan Allahi wa bi Hamdihi (Glory be to Allah the Almighty, Glory and praise be to Allah.” Al-Bukhaari (6406) and Muslim (2694).
It was narrated from Juwayriyyah that the Prophet (blessings and peace of Allah be upon him) left her house one morning when he prayed Fajr, and she was in her prayer-place, then he came back after the forenoon had come, and she was still sitting there. He said: “Are you still as you were when I left you?” She said: Yes. The Prophet (blessings and peace of Allah be upon him) said: “After I left you I said four words three times, which if they were weighed against what you have said today, they would outweigh it: Subhaan Allah wa bi hamdih, ‘adada khalqihi, wa ridaa nafsihi, wazinata ‘arshihi, wa midaada kalimaatihi (Glory and praise be to Allah, as much as the number of His creation, as much as pleases Him, as much as the weight of His Throne and as much as the ink of His words).” Narrated by Muslim, 2726.
3. Regularly reciting adhkaar after the obligatory prayers
It was narrated from ‘Abdullah ibn ‘Amr that the Prophet (blessings and peace of Allah be upon him) said: “There are two deeds that a Muslim does not do regularly but he will enter Paradise. They are easy but those who do them are few; saying Subhaan-Allah ten times after every prayer, and saying al-hamdu Lillaah ten times, and saying Allahu akbar ten times. That makes one hundred and fifty on the tongue and one thousand and five hundred in the Balance. And saying Allahu akbar thirty-four times when going to bed, and saying al-hamdu Lillaah thirty-three times, and subhaan-Allah thirty-three times. That is one hundred on the tongue and one thousand in the Balance.”
Narrated by Ahmad (6616), Abu Dawood (5056), at-Tirmidhi (3410), an-Nasaa’i (1331) and Ibn Maajah (926). Classed as saheeh by Shaykh al-Albaani in Saheeh at-Targheeb wa’t-Tarheeb.
4. Patience and seeking reward with Allah upon the loss of a righteous child
It was narrated from Zayd, from Abu Salaam, from the freed slave of the Messenger of Allah (sa) (blessings and peace of Allah be upon him) that the Messenger of Allah (sa) (blessings and peace of Allah be upon him) said: “Excellent, excellent, for there are five things, how heavy they are in the balance: Laa ilaaha ill-Allah, Allahu akbar, Subhaan-Allah and al-hamdu Lillah, and the death of a righteous child whose parents seek reward (for their loss, with Allah). Excellent, excellent, for there are five things, whoever meets Allah believing with certainty in them, will enter Paradise: belief in Allah, the Last Day, Paradise and Hell, the resurrection after death, and the reckoning.”
Narrated by Imam Ahmad (15107); classed as saheeh by Shaykh al-Albaani in as-Silsilah as-Saheehah.
5. Good attitude
It was narrated from Abu’d-Darda’ that the Prophet (blessings and peace of Allah be upon him) said: “There is nothing that weighs more heavily in the Balance than a good attitude (with people).” Narrated by Abu Dawood (4799); classed as saheeh by Shaykh al-Albaani (may Allah have mercy on him) in Saheeh Abi Dawood.
It was narrated from Umm ad-Darda’, from Abu’d-Darda’ who said: I heard the Prophet (blessings and peace of Allah be upon him) say: “There is nothing that is placed in the balance that will weigh more heavily than a good attitude (with people); the one who has a good attitude will attain thereby the status of one who fasts and prays.”
Narrated by at-Tirmidhi (2003); classed as saheeh by al-Albaani (may Allah have mercy on him) in Saheeh at-Tirmidhi.
6. Attending a funeral until the burial is completed
It was narrated from Ubayy that the Prophet (blessings and peace of Allah be upon him) said: “Whoever attends a funeral until the prayer has been offered for the deceased and the (burial) is completed will have two qiraats (of reward), and whoever attends until the prayer has been offered will have one qiraat. By the One in Whose hand is the soul of Muhammad, it will weigh more heavily in his balance than Uhud.” Narrated by Imam Ahmad (20256); classed as saheeh by Shaykh al-Albaani in Saheeh al-Jaami‘ as-Sagheer.
And Allah knows best.