Q. Which is better - to wear one's long (but old) weekday tzitzis on Shabbos, or wear Shabbos tzitzis that have a proper shiur and which are clean and new, but the Shabbos tzitzis are too short to be seen under one's long jacket worn on Shabbos and therefore one is not able to comply with the idea of having one's tzitzis be visible?
A. Shulchan Aruch (O.H. 8: 11) writes that the main mitzva of a taalis kotton is to wear it over his cloths, so he will always see it and remember the mitzvos. Mishna Berura (ibid. 11) quotes Magen Avrohom and Kisvei Hoarizal, that the taalis itself should be covered but the tzitzis should be seen outside.
Vayoshov Hayom (3: 4: p. 387) quotes Chida, Sheloh and others, that the bottom tip of the tzitzis should be seen under the coat (meil). Yalkut Yosef (8: p. 99) mentions that it suffices if they are seen when sitting down.
Horav Shlomo Miller's Shlit'a opinion is that one does not need to have his tzitzis protruding from under a long coat, a raincoat or a winter coat, worn during the week or on Shabbos, as is the common and normal custom of many.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller Shlit'a
Important Numbers
