It will be legally correct to say that: he should be OT wages for 4 shifts. (3 worked+ 1 off day). If you follow comp-off practice for such working (it is not legally correct to do so) then he should be given 4 comp-offs.
Please clarify on following points --
a) Why was employee called for 3 shifts in a day ?
b) Who called him ?
c) What your company's shift policy says ?
This is for your information that if someone is being called off for a extra work on his off days, he /she is should be a given compensatory off against any leave availed by later.
Also, suggest you to be clear in drafting and executing company's policies as they help you and employees for one ground of understanding and also further calculation of comp. off.
Hope this will help you.