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

Hadith n. 96
Amir al-mu’minin, peace be upon him, said: The persons most attached to the prophets are those who know most what the prophets have brought. Then Amir al-mu’minin recited the verse: Verily, of men the nearest to Abraham are surely those who followed him and this (Our) Prophet (Muhammad) and those who believe (Qur’an, 3:68).
Then he said: The friend of Muhammad is he who obeys Allah, even though he may have no blood relationship, and the enemy of Muhammad is he who disobeys Allah even though he may have near kinship.

Hadith n. 97
Amir al-mu’minin, peace be upon him, heard about a Kharijite who said the mid-night prayers and recited the Qur’an, then he said: Sleeping in a state of firm belief is better than praying in a state of doubtfulness.

Hadith n. 98
Amir al-mu’minin, peace be upon him, said: When you hear a tradition, test it according to the criterion of intelligence, not that of mere hearing, because relaters of knowledge are numerous but those who guard it are few.

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