Many newcomers to Shabat observance have probably had this experience: You go to wash hands with everybody else, go back to your seat and happily chat up your neighbour until you notice that she/he is not answering and/or you are the only person in the room still speaking. Ouch. So you have just learned that the custom is not to speak from hand washing (netilat yadaim) until the blessing over bread (hamotzi) is said.
Where is the source for that? I just stumbled upon a mention in the Kizzur:
Care should be taken not to have an interruption between washing hands and ”who brings forth bread” [the blessing over bread].
(Kizzur shulchan aruch 41:2)
According to Rabbi Josh Flug at YUTorah the actual basis in the Talmud is in Berachot 42a, I assume he meant this one sentence:
Grace should follow immediately on the washing of hands.
There seems to be a doubt if this sentence actually refers to washing before the meal or after the meal. Among others, the Rambam actually allows speaking, but the recommended procedure nowadays seems to be that it is preferred not to (Halacha Yomit).