He, sallallaahu ‘alayhi wa sallam, instructed them not to be hard on themselves in worship:
Anas (a Companion) narrated that the Messenger of Allah, sallallaahu ‘alayhi wa sallam, entered the mosque and found a rope tied between two of its pillars; so he, sallallaahu ‘alayhi wa sallam, asked: “What is this?” People said: ‘It is for Zaynab. She prays and when she slackens or feels tired she holds it.’ Upon this the Messenger of Allah, sallallaahu ‘alayhi wa sallam, said: “Untie it. Let one pray as long as one feels fresh but when one becomes tired one must stop it.””
An-Nawawi (a scholar) said: “This narration is evidence that one should not be hard on himself in worship and should be balanced, and that one should perform the acts of worship when they are energetic and as soon as one feels tired, they should stop and resume once they regain energy.