Avodah Zarah

BUT A KNIFE MAY BE POLISHED AND IS THEN RITUALLY CLEAN. R. 'Ukba b. Hama said: One plunges it ten times in soil.  R. Huna the son of R. Joshua said: That is, in untilled soil. R. Kahana said: [This holds good only] of a knife which is in sound condition and has no notches. It has been also taught to the same effect: With a knife in sound condition and without notches one plunges it ten times in soil. R. Huna the son of R. Joshua said: [This holds good only] to eat cold food with it.  Thus Mar Judah and Bati b. Tobi were sitting with King Shapur and a citron was set before them. [The king] cut a slice and ate it, and then cut a slice and handed it to Bati b. Tobi. After that he stuck [the knife] ten times in the ground, cut a slice [of the citron] and handed it to Mar Judah. Bati b. Tobi said to [the king], 'Am I not an Israelite!' He replied, 'Of him I am certain that he is observant [of Jewish law] but not of you.' According to another version he said to him, 'Remember what you did last night!'