Tosefta for Bekhorot 60:7

[With respect to one who] comes to take upon himself [the obligations of a chaver, see Minchat Yitzchak here], if he had always [lit. "from the beginning"] acted modestly, we accept him, and afterwards we teach him [the strictures applicable to the chaverim], and if not (i.e., if he had not always been modest), we teach him first, and afterwards we accept him. [Rabbi Shimon says, either way we accept him first and then we teach him (per the GR"A)], and we lead him (i.e., impart the halachot on him) like so: [First] we accept him regarding "wings" (the ritual washing of hands before eating, see Y. Dem. II.3.7), and after than we accept him regarding "purities" (eating ritually clean food, ibid.). And if [at that point] he said, "I don't take this (i.e., "purities") upon myself, but only "wings," we still accept him. If he takes upon himself "purities" but does not take upon himself "wings," then he is not [considered] trustworthy. How long until we accept him [as a chaver]? Beit Shammai say, 30 days as to [matters of impurity involving] liquids, 12 months as to [the impurity of] clothing. And Beit Hillel say, 30 days for both.