Because Allah, the Exalted, has said: «وتلك الجنة التي أورثتموها بما كنتم تعملون‏» "And this is Paradise, which you have been made to inherit because of what you used to do." And many of the scholars, in the explanation of the statement of Allah, the Exalted: «فوربك لنسألنهم أجمعين عما كانوا يعملون‏» etc., say that here "action" means to say «لا إله إلا الله» . And Allah, the Exalted, has said: "Those who do should do the like of it."

Narrated Abu Huraira: Allah's Apostle was asked, "What is the best deed?" He replied, "To believe in Allah and His Apostle (Muhammad). The questioner then asked, "What is the next (in goodness)? He replied, "To participate in Jihad (religious fighting) in Allah's Cause." The questioner again asked, "What is the next (in goodness)?" He replied, "To perform Hajj (Pilgrim age to Mecca) 'Mubrur, (which is accepted by Allah and is performed with the intention of seeking Allah's pleasure only and not to show off and without committing a sin and in accordance with the traditions of the Prophet)."