I am not currently aware of a Hadith where it is mentioned that the Holy Prophet Sallallahu Alaihe Wa Sallam cooked for his family but it is certainly true that the Holy Prophet Sallallahu Alaihe Wa Sallam always helped his family in the household work.
It is not the wife's duty by Islamic law to cook for the family but with mutual understanding the husband and wife work together the make the family a happy and successful family by sharing the responsibilites and by dividing the jobs also.
And Allah knows best.
Fatwa Center of America
10 Jumada-al Ukhra 1432/ May 14 2011