Serving mother-in-law

Hakim al umma Hadhra Mawlana Ashraf ‘Ali Thanawi (may Allah have mercy on him) said, 

“Understand this thoroughly; it is not essential (wajib) for the wife to serve her mother-in-law. If you are a caring son, provide service to her yourself or get a servant to do so.” 

Islah inqelab, volume 2, page 188, via Tohfa zojain page 24