It does not befit a Muslim to overburden himself with work to the extent that it violates the rights of his soul, the rights of his family, and the rights of his society. This applies even if such exertion is in the worship of Allah, be it by way of fasting, Salah, sacrifice, or abstinence.
It is for this reason that the Prophet, peace be upon him, when he saw his Companions ever congregating behind him for the night vigil, said to them: "Take from work what you can, for verily Allah does not stop (rewarding you) until you get fed up (in worshipping Him); and verily the most beloved of works to Allah is that which is most constant even if it is meagre." [Bukhari, Muslim]
In another instance he said: "Verily this Religion (of Islam) is very easy. No one ever challenges this Religion but it overcomes him. So be moderate, and try to approach perfection, and receive the glad tidings." [Bukhari]
This, therefore, is the sunnah (i.e. constant practice) of the Prophet, peace be upon him, and this is his method: an open, plain, easy road of moderation and observance of balance between spiritualism and materialism; an equilibrium between the requirement of the self and the right of the Lord.
"Time in the Life of a Muslim" - Yusuf Al-Qaradawi, pp. 29, 30