פירוש על ברכות 59:2

HOW DOES HE RECITE [THIS PRAYER]? The Gemara asks how one prays t’feelas haderech? The Gemara’s question, how does one pray this prayer, refers to the prayer of t’feelas haderech. And Rav Shaishes says that one may recite this prayer even as he walks. And the Halochoh is in accordance with Rav Shaishes. However in the Tosfos¹This emendation is found in the Tosfos of Rabainu Yehudoh the pious. of HoRav Yosaif he ruled in accordance with Rav Chisdo. And so too Rav Alfas said that he prefers Rav Chisdo’s opinion better than Rav Shaishes’ opinion, because we see that even Rav Shaishes did as Rav Chisdo when he had the opportunity and referred to Rav Chisdo’s opinion as being better.

The question is capable of two interpretations : (1) Up to what distance may a man go without saying the prayer, and if he exceed it, bis prayer becomes invalid ? (2) What is the minimum distance which constitutes a journey necessitating the prayer?