Sign Of Sickness In The Heart

Hadrat [1] Imam-i Rabbani says in the 17th letter of the third volume of his Maktubat:

Not to do the commandments of Allahu ta'ala is caused by a sickness in the heart. A sickness in the heart means that it does not believe in the Shari'at [2]thoroughly. To be a Believer, it is not enough only to express the word Shahadat [3] (Ash hadu an la ilaha illallah wa ashhadu anna Muhammadan abduhu wa rasuluhu. . . ). Munafiqs (those who pretend to be Muslims though being disbelievers) also express it. The sign of the existence of iman in the heart is to do the commandments of the Shari'at willingly. To give one gold coin to a poor Muslim with the intention of zakat (alms giving) is more blessed than giving a hundred thousand gold coins as alms, because to give zakat is to obey the Shari'at's command. But those that are given without the intention of zakat are supererogatory worships. Supererogatory worships are of no value when compared to fard worships. They are not even like a drop of water compared to an ocean. The Devil, by deceiving Muslims, prevent them from performing their omitted salats. Performing the supererogatory salats [4], [supererogatory pilgrimage, and umra] are made to appear more beautiful. Also, by misrepresenting supererogatory deeds and actions as beautiful, he prevents them from giving zakat. [The promised great rewards for the sunnats [5] and for the supererogatory are for those who do not owe fard deeds and who have paid their omitted fard [6] worships. But those who still have omitted fard worships will not be given any rewards for any worships besides the fard ones.]

[1] Hadrat: title of respect used before the names of great people like and Islamic scholars.
[2] Shari'at: (pl. of Shari'a) i) rules and commandments as a whole of the religion. ii) religion.
[3] kalimat ash-shahada: the phrase beginning with "Ashhadu..." The first of the five fundamentals of Islam; declaring one's belief in Islam.
[4] salat: i) prayer; (with salam)= salawat; ii) ritual prayer of at least two rak'as; "namaz", in Persian; salat janaza: funeral prayer.
[5] sunnat: i) (when used alone) The Shari'at; ii) (when used together with the name Book) The hadith of the Prophet. iii) (when used together with the word Fard) Any action, word or thought liked and commanded by the Prophet.
[6] fard: an act or thing that is commanded by Allahu ta'ala in the Qur'an al-karim. Fard (or fard) means (any behaviour or thought or belief which is) obligatory. Islam's open commandments are called fard (pl. faraid).