Sahih Muslim Book 6, Hadith Number 2435.

Chapter : It is forbidden to observe uninterrupted fasting.

‘Aisha (Allah be pleased with her) said: The Apostle of Allah (may peace be upon him) forbade them (his Companions) to observe Saum Wisal out of mercy for them. They said: You (Holy Prophet) yourself observe it. Upon this he said: I am not like you. My Lord feeds me and provides me drink.