then why when the voltage of the resistor compound with "say collector" is bigger than the voltage of the source we say that the transistors is in the saturation state ?
You say voltage of (I assume you mean across), is a current?
In this circuit, the current through Rc can be no more than 12mA. When the transistor is saturated, Vce would be close to 0V. That means both junctions are forward biased.