The Babylonian Talmud on Amulets on the Sabbath

Nor [go out] with an amulet unless [ made] by an expert.

[Aramaic] R. Papa said: This does not imply that the man [who produced it] has to be an expert [for it to be an] expert amulet. Rather, if the man is an expert but the amulet is not expert [i.e., proven, one may go out with it].

But it is already explicitly stated [in the mishnah]: Nor with an amulet unless [made] by an expert. And it is not stated: “If it is not an expert [proven] amulet.”

Learn from this. The sages taught [in a baraita]: [Hebrew] What is an expert amulet? Any that has healed two or three times—whether it is a written amulet or an amulet with roots; whether [healing] a sick person in danger, or a sick person not in danger. Not [only] that [someone] has fallen [ill], but lest someone fall [ill]. Thus, one may tie and untie it even in the public sphere [on the Sabbath], but one may not tie [the amulet] to a bracelet or ring and go out into the public sphere, because of [its] “appearance” [misinterpreted as a transgression that is permissible].

But has it not been taught: What is an expert amulet? Any that has healed three people as one [and the same]. [There is] no difficulty [here]. This [case] is to prove the expertise of the man [who made it], and that [case] to prove the expertise of the amulet [itself]. R. Papa said: This is obvious to me. Three amulets for three people, each healing three times—thus, the man is proven, and the amulet is proven [effective]. Three amulets for three people [healing] each only one time—the man is proven, but the amulet is not proven [effective]. One amulet for [healing]—the amulet is proven [effective], but the man is [still] not proven [an expert].

[Aramaic] R. Papa raised a question: Three amulets for one person—what is the case? The amulet is certianly not proven [effective]. But is the man a proven expert or not? Shall we say: Did this [amulet] heal him, or was it just luck for this very man who received the writing [on the amulet]? Unresolved.