Maliks Muwatta Book 18, Hadith Number 38.

Section : The Prohibition against Fasting for Two Days or More without Breaking the Fast in between (Wisal).

Yahya related to me from Malik from Nafi from Abdullah ibn Umar that the Messenger of Allah, may Allah bless him and grant him peace, forbade fasting for two days or more without breaking the fast in between. They said, “But Messenger of Allah, you practise wisal.” He replied, “I am not the same as you. I am fed and given to drink.”