Dear Dario, i recently sold my house. and after signning the S&P, i decided to withdraw it.  At that point of time, the S&P was not stamped yet, and i called my lawyer and ask whether i can abort the transaction since it is not stamped yet. But according to my lawyer, he said that the S&P is valid although it is not stamp, and the purchaser wil have the right to ask for penalty from me.   Is that correct?

thanks

Yes. That is correct. The purchaser has the right to compel you to proceed with the transaction.