Sahih Muslim Book 6, Hadith Number 2431.

Chapter : It is forbidden to observe uninterrupted fasting.

Abu Huraira (Allah be pleased with him) reported Allah’s Apostle (may peace be upon him) as saying (the words as said in the previous Hadith) but with this alteration (of words): “Take upon yourselves (the burden of the deeds) for which you have the strength to bear.”