Al-Imam Ali (p.b.u.h), said:

Hadith n. 39

Amir al-mu’minin, peace be upon him, said: Supererogatory worship cannot bring about nearness to Allah if it hampers the obligatory.

Hadith n. 40

Amir al-mu’minin, peace be upon him, said: The tongue of the wise man is behind his heart, and the heart of the fool is behind his tongue.

As-Sayyid ar-Radi says: This sentence has a strange and beautiful meaning. It means that the wise man does not speak with his tongue except after consulting his mind and exercising his imagination, but the fool quickly utters whatever comes to his tongue without thinking. In this way, the tongue of the wise man follows his heart while the heart of the fool follows his tongue.

Hadith n. 41

This very sense has been related from Amir al-mu’minin, peace be upon him, in a different version as follows:

The heart of a fool is in his mouth while the tongue of the wise man is in his heart.

The meaning of both the sayings (40 and 41) is the same.

Hadith n. 42

Amir al-mu’minin, peace be upon him, said to one of his companions during his sickness:

May Allah make your illness a means for writing off your sins, because there is no reward for sickness but that it erases sins and makes them fall like (dried) leaves. Reward lies in saying by the tongue and doing something with the hands and feet. Certainly, Allah, the Glorified, admits into Paradise by virtue of truthfulness of intention and chastity of heart to whomsoever He wishes from among His creatures.

As-Sayyid ar-Radi says: Amir al-mu’minin is right in saying that there is no reward for sickness as such because compensation is admissible in respect of the acts of Allah, the Sublime, towards his creatures such as grief, illness and the like, whereas reward and recompense becomes admissible against actions by the creature. This is the difference between the two and Amir al-mu’minin has clarified it through his lustrous knowledge and sound view.

Source: https://www.al-islam.org/nahjul-balagha-part-2-letters-and-sayings