Driving S or C mode does S put more strain on the car
 

I heard someone told me after break in period try not to drive in S mode all the time. S mode puts more stress on the car than c mode. Will this cause more wear and tear for thecar or is it a mercedes made to be driven hard and fast. What do you think should one drive in S mode all the time or this bad for the car.

S mode is the normal driving mode. It does not put any unecessary strain on your car.

The owner's manual recommends that you actually drive in C-mode for the initial break-in period.

The rational behind this is that the C-mode has a much less aggressive downshift pattern. It doesn't downshift as much when you're passing nor when you're braking. Downshifting is somewhat stressful on the transmission.

My recommendation is to put it in S-mode and drive carefully to avoid excessive downshifts.

On which page of the owner's manual?, I tried to find this on the owner's manual but I did not see it. can you please tell me?

I think it's actually the opposite. C mode puts more strees onto your engine and tranny. While it's not significantly more it is a bit more. The reason behind it is in C mode (Comfort) you car will start from 2nd gear and will give you a much smoother ride but not downshifting until necessary. In S mode (Sport) your car starts out in 1st gear and revs the RPMs pretty higher then C mode and downshift more often in C mode.
With all this said I still prefer to drive my car in C mode. During my morning commute I sit in a lot of traffic and C mode stop and starts are much more pleasent then S mode starts and stops. Once time in S mode during bumper to bumper traffic my dog actually threw up in the car. She has never done that in C mode.
I really don't think it makes a HUGE difference in what mode you are in. Benz's are supposed to give you a nice comfy ride but are also OK to drive hard and fast. Just make sure during the break-in period to leave it in C mode until the engine settles in.