All praise is due only to Allaah. We laud Him and beseech His

The extent to which a husband can strike his wife
If this second stage of rectification did not work, then the 
husband can proceed to the third stage. He should strike her. 
But how is he to strike her? And to what extent? 
Regarding this, on the occasion of Hajjatul Widaa, amongst all 
the other advices, Nabi (sallallahu alayhi wasallam) also gave 
this advice, 
“And when you (need to) hit them, then strike them 
such that it is not violent, intense or painful.”
The first stages 
are first to be explored and this is the final and last stage when 
there is no other way left. The Shariah has also stipulated the 
condition that when the husband strikes his wife it should not 
be painful for her. The actual object of striking her is to make 
her aware of her folly and the purpose is not to maim her or 
even cause the slightest pain. 
Nabi (sallallahu alayhi wasallam) treatment of his wives
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At the time when our beloved Nabi (sallallahu alayhi wasallam) 
passed away, he left nine wives. These blessed wives of Nabi 
(sallallahu alayhi wasallam) were not angels who fell from the 
heavens. They were normal women and the usual rivalry which 
is natural between co-wives also took place amongst them. The 
issues which normally spring up between husband and wife 
also occurred to Nabi (sallallahu alayhi wasallam) and his 
wives. Hadhrat Aishah (radhiallahu anha) says that not only did 
Nabi (sallallahu alayhi wasallam) never lift his hand on any 
female his entire life, but whenever he entered the home, he 
would do so smiling. 
The Sunnat of Nabi (sallallahu alayhi wasallam) 
The Sunnat of our Nabi (sallallahu alayhi wasallam) was this 
that he never ever struck any woman. Although there is consent 
to strike the wife, nonetheless, this is only in extreme 
circumstances. But better than that is to practice on the Sunnat 
of Nabi (sallallahu alayhi wasallam), which is never to strike a 
woman, and to always enter the home smiling.