אמר רב נחמן: תיתי לי דקיימית שלש סעודות בשבת. אמר רב יהודה: תיתי לי דקיימית עיון תפלה. אמר רב הונא בריה דרב יהושע: תיתי לי דלא סגינא ארבע אמות בגילוי הראש. אמר רב ששת: תיתי לי דקיימית מצות תפילין. ואמר רב נחמן: תיתי לי דקיימית מצות ציצית
R. Nahman said: "May [reward] come to me for observing three meals on the Sabbath." R. Yehudah said: "May [reward] come to me for observing focus in prayer. R. Huna son of R. Joshua said: May [reward] come to me for never walking four cubits bareheaded. R. Sheshet said: May [reward] come to me for fulfilling the commandment of tefillin. R. Nahman [also] said: May I be rewarded for fulfilling the commandment of tzitzit.
Commentary:This passage connects statements from various rabbis that indicate that the fulfillment of certain practices deserves reward. The collection seems united by the phrase "תיתי לי", especially since there is no pttern or unity in the sages' era- they come from several different generations of Amoraim.
First, this implies that doing so is unusual and/or difficult. Second, the combination suggests that all have some shared value. However, some are clear, d'oraita (from the Torah) mitzvot- tzitzit, tefillin. (One wonders that these were seen as deserving of particular praise- it says Something about how little the Jewish people may have changed over time.) Others are pietistic practices/abilities- maintaining focus in prayer, and not going bare-headed. Yet focus in prayer is really part of the mitzvah of prayer- the best way to fulfill the mitzvah, possibly the only way. Whereas head-covering is only piety, not a mitzvah at all...
The obvious connection (to me at least) is that these are difficult and/or unusual practices which the rabbis would like to encourage- yet in this context go no further than saying that they will bring eventual reward. Not exactly a statement of requirement in regards to head-covering, but the way that the statements have been brought together by their common structure begins to give it a weight that it does not have on its own.