6th Hadith of An-Nawawi's Forthy Hadiths
On the authority of Al-Numan bin Basheer, who said : I heared the messenger of Allah say :
"That which is lawful is plain and that which is unlawful is plain and between the two of them are doubtful matters about which not many people know. Thus he who avoids doubtful matters clears himself in regard to his religion and his honor, but he who falls into doubtful matters falls into that which is unlawful, like the shepherd who pastures around a sanctuary, all but grazing therein. Truly every king has a sanctuary, and truly Allah's sanctuary is His prohibitions. Truly in the body there is a morsel of flesh which, if it be whole, all the body is whole and which, if it be diseased, all of it is diseased. Truly it is the heart."
(Narrated by Bukhari and Muslim)
There are doubtful matters that a Muslim might face in his/her everyday dealings and activities. This hadith helps the Muslim in dealing with such matters. There is an early ongoing preparation which is needed in such a case - to purify one's heart.
There are some actions that can help us achieve this task, like: hayya' (modesty), murakabah (self reckoning), muhasabah (self accountability), dzikr (remembrance of Allah), and as-Salatu 'ala an-Nabi, sallallahu 'alayhi wasallam. These are things that, insha Allah, can help us and enlighten and purify our heart, and also help us to identify and avoid the doubtful matters - this is the main point, the key, the principle of the hadith.
"Truly in the body there is a morsel of flesh which, if it be whole, all the body is whole and which, if it be diseased, all of it is diseased. Truly it is the heart."