$\displaystyle\int \left[ \nabla \times \dfrac {M(r')}{r} \right] d\tau =\oint \dfrac{1}{r} \left[ M(r')×da' \right]$
I came across this integral from the David Griffiths introduction to electrodynamics, page no 278 ,fourth edition . But I really don't understand the procedure they came up with. It would be a great help if someone explains it step by step.