It is always stated in islamic sites etc that men's awrah is from knees to navel. (for example http://islamqa.info/en/34976 ).
I have searched hadithes about that, and I have found many hadithes about covering thigh, you can see them in the url or in http://sunnah.com/search/?q=thigh , but I have found almost none hadithes that clearly prove that chest (torso, trunk) is not awrah, I have found 1 hadith: http://sunnah.com/tirmidhi/42/45 , in which somebody sees prophet naked in his house.
We can think that if that was awrah, prophet should say about it, and if he did not say, then it is tolerable. but the hadith does not clearly say that prophet did not say about it, we just can think so, because the hadith does not say about it, and since it is important thing, its narrators should not leave that hidden, so we think the prophet did not say anything about that, so we decide it is not awrah. but there is probability that it was so much clearly known by everybody, that chest is awrah, so it was even not told in the narration.
Awrah might be exposed by mistake and just who see it might must look at other direction or close his eyes or cover the awrah by hands etc.
So, are there any other hadithes which show that some men at time of Muhammad showed their torso for long time and it was allowed or was not prohibited? Ie can you prove or disprove the decision of fakihs that chest is not awrah? Or can you say by hadithes that seems nobody showed his chest so that can be considered as proof that it is awrah?
(Some illustration for that it is desicion of fakihs: http://islamqa.info/en/171584 : "And he said in ash-Sharh al-Kabeer, 1/457: The navel and the knees are not part of the ‘awrah. This is the view of Maalik and ash-Shaafa‘i. End quote.")