Rav Shimon Schwab zt"l (in an audio shiur titled "Jews in Golus - How High A Profile") quoted a tosefta in perek hagozel which says that to steal from a non-Jew is worse than stealing from a Jew for he doesn't have a kaparah (chance at atonement) ever, if the he dies before doing teshuva.
Does anyone know where this tosefta is located?