´It was narrated from Abu Hurairah that:` The Messenger of Allah [SAW] was asked: "Which deed is best?" "He said: Faith in Allah [SWT] and His messenger [SAW]."
Hadith Referenceسنن نسائي / كتاب قطع السارق / 4988
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:متفق عليه
1؎: The literal meaning of iman is affirmation, and in the terminology of the Shari‘ah, iman is: verbal declaration, affirmation by the heart, and action by the limbs and organs. Furthermore, the belief that iman increases with obedience and decreases with disobedience is the creed of the Salaf. And iman is the best of all deeds because all good and righteous actions and deeds depend upon iman; if there is no iman, then no righteous deed will be accepted. In many ahadith, various actions have been described as «أفضل عمل» (“the best deed”), so (after iman) the answer was given according to the specific circumstances and background of the questioner or the time of questioning.
Explanation & Benefits
Hafiz Muhammad Ameen
(1) "To have faith (iman)"—this act is the root of faith, without which the very concept of the tree of faith and Islam cannot even be imagined. And without it, no righteous deed is of any benefit. When this faith exists, entry into Paradise is certain, whether immediately or after undergoing punishment. In this hadith, faith (iman) has been described as an action. This supports the view of the hadith scholars (muhaddithin) who consider actions to be a part of faith.
(2) In the Qur'anic verses, faith (iman) and righteous deeds (amal salih) are mentioned separately due to the importance of actions, just as, owing to the significance of the Asr prayer, there is a specific command to guard it separately: (Guard strictly the prayers, especially the middle prayer) (: al-Baqarah 2:238).
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 4988