Musannaf Ibn Abi Shayba 33:1249

Yazid ibn Harun narrated to us, he said: Ibn 'Awn and Hisham both informed us, from Muhammad ibn Sirin, who said: We were with Abu Ubaydah ibn Hudhayfah in a tent of his, when a man came to him and sat with him on his bedding. He whispered something to him that I did not understand. Abu Ubaydah said to him: "I ask you to put your finger into this fire," and there was a brazier between them containing fire. The man said: "Subhan Allah!" Abu Ubaydah said: "You are stingy with me regarding one of your fingers in the fire of this world, yet you ask me to place my entire body into the fire of Hell?" He (Ibn Sirin) said: We thought that he had invited him to [accept] the position of judge.