Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates that the Prophet (peace and blessings be upon him) said: "Indeed, the self grows weary, and none of you knows the length of his term (how much life he will be granted). So a person should consider how much worship he is able to sustain, and then do it regularly, for the most beloved deed to Allah Almighty is the one done regularly, even if it is little."
This narration was recorded by Imam al-Tabarani in al-Mu'jam al-Awsat; its chain contains a narrator, al-Jarud bin Yazid, who is matruk (abandoned).