Musannaf Ibn Abi Shaybah

Hasan (may Allah have mercy on him) narrates that Hazrat Abu Barzah (may Allah be pleased with him) said: We were participating in a certain battle. We encountered a few people from among the polytheists. We stopped them from eating bread that was baked on hot ashes, but then we ourselves got involved in it and started eating it as well. And in the days of ignorance, we used to hear that whoever eats bread becomes fat. So when we ate that bread, each one of us would look at himself to see whether he had become fat.