Sahih Muslim
The Book of Destiny (Kitab-ul-Qadr)
Book Number: 033 / Hadith Number: 6419
Tawus reported: I found some Companions of Allah's Messenger (may peace be upon him) as saying: Everything is by measure. And he further said: I heard Abdullah b. 'Umar as saying: There is a neasure for everything-even for incapacity and-capability.