Allah does not impose upon any soul a duty but to the extent of its ability; for it is (the benefit of) what it has earned and upon it (the evil of) what it has wrought: Our Lord! do not punish us if we forget or make a mistake; Our Lord! do not lay on us a burden as Thou didst lay on those before us, Our Lord do not impose upon us that which we have not the strength to bear; and pardon us and grant us protection and have mercy on us, Thou art our Patron, so help us against the unbelieving people."
Al-Baqra Verse 286
Allah's Apostle said, "If I had not found it hard for my followers or the people, I would have ordered them to clean their teeth with Siwak for every prayer."
Sahih Bukhari: Volume 2, Book 13, Number 12