Explanation of the words of Imam al-Nawawi (may Allah have mercy on him) regarding what he quoted: "

The Shaykh : For this reason, Sufyan ibn 'Abdullah al-Bajali (may Allah be pleased with him) asked the Prophet (peace and blessings be upon him) a question, saying: “Tell me a word about Islam such that I will not ask anyone else about it”, meaning a word that is sufficient, comprehensive, and complete, such that I would not need to ask anyone else. He said: Then be steadfast upon His religion and His Shari'ah. This is the word the Prophet (peace and blessings be upon him) said to the one who said to him: “Tell me a word about Islam such that I will not ask anyone else about it”. So, my brother, accept the advice of the Prophet (peace and blessings be upon him): say “I have believed in Allah,” then be steadfast upon the religion of Allah. This will bring you happiness in this world and the Hereafter. And success is from Allah.
The reader: In the name of Allah, the Most Gracious, the Most Merciful.
Praise be to Allah, Lord of the worlds, and may peace and blessings be upon our Prophet Muhammad, and upon his family and all his Companions.
The author (may Allah have mercy on him) quoted: “From Sufyan ibn 'Abdullah (may Allah be pleased with him), who said:

he said, "Messenger of God, say something about Islam concerning which I shall need to ask no one after you are gone.” (A version has "anyone else”.) He said, "Say, ‘I believe in God’, then keep to the straight path.”

قلت يا رسول الله قل لي في الإسلام قولا لا أسأل عنه أحدا غيرك قال قل آمنت بالله ثم استقم

Mishkat al-Masabih 15Sahīh (Zubair `Aliza'i)

Narrated by Muslim”

The Shaykh : In the name of Allah, the Most Gracious, the Most Merciful.
This chapter we are in is the chapter of steadfastness (istiqamah). We have previously explained its meaning and the meanings of the verses that mention it. As for the hadiths, the author (may Allah have mercy on him) mentioned that Sufyan ibn 'Abdullah (may Allah be pleased with him) said: “O Messenger of Allah, tell me a word about Islam such that I will not ask anyone else about it”, meaning tell me a word that is decisive and conclusive, such that one does not need to ask anyone else. The Prophet (peace and blessings be upon him) said to him: Say: . By his saying (peace and blessings be upon him): , it is not meant merely the utterance of the tongue, for among people are those who say “We have believed in Allah and the Last Day,” but they are not believers. Rather, it means the statement of the heart and the tongue as well, meaning that a person should say it with his tongue after he has affirmed it in his heart and held it as a firm belief with no doubt in it. This is because faith in the heart alone is not sufficient, nor is faith in the tongue alone sufficient; it is necessary to have faith in both the heart and the tongue. For this reason, the Prophet (peace and blessings be upon him) used to say when calling people to Islam: . He said: Say with your tongues, just as it is necessary to say it with the heart. And his saying: includes belief in the existence of Allah (Mighty and Majestic), in His Lordship, in His names and attributes, in His rulings, in His reports, and in everything that comes from Him (Mighty and Majestic); you believe in all of it. If you believe in that, then be steadfast upon the religion of Allah. Be steadfast upon it, meaning do not deviate from it, neither to the right nor to the left, do not fall short, and do not add to it. Be steadfast upon the religion, be steadfast upon the testimony that there is no god but Allah and that Muhammad is the Messenger of Allah, and do so by being sincere to Allah (Mighty and Majestic) and following His Messenger. Be steadfast upon the prayer, be steadfast upon the zakah, be steadfast upon fasting, be steadfast upon Hajj, and be steadfast upon the entire Shari'ah of Allah. In his saying (peace and blessings be upon him): , there is proof that steadfastness does not occur except after faith, and that one of the conditions for the validity and acceptance of good deeds is that they be built upon faith. If a person acts outwardly as it should be, but his inner state is ruined, in doubt, in turmoil, or in denial and refutation, then that will not benefit him.
For this reason, the scholars (may Allah have mercy on them) agreed that one of the conditions for the validity and acceptance of worship is that a person be a believer in Allah, meaning that he acknowledges Him and everything that has come from Him (Blessed and Exalted is He).
It is also derived from this hadith that a person should, when performing an act, feel that he is performing it for Allah, that he is performing it by Allah, and that he is performing it in Allah. This is because one does not become steadfast upon the religion of Allah except after believing in Allah (Mighty and Majestic). So he feels that he is doing it for Allah, meaning with sincerity; by Allah, meaning seeking His help; and in Allah, meaning following His Shari'ah. This is derived from the saying of Allah the Exalted: . The first is standing for Allah, the second is standing by Allah, and the third is standing in Allah, meaning in His Shari'ah. For this reason, we say that the straight path (al-sirat al-mustaqim) in the noble verse refers to the Shari'ah of Allah (Mighty and Majestic) that leads to Him. And success is from Allah.