Ketubot

and as witnesses can be rebutted only in their presence,  so can they be contradicted only in their presence.  R. Nahman said to him: If they  had been before us and [the other two witnesses] had contradicted them, it  would hake been a contradiction,  and we would not have paid any attention to them,  because it  is a contradicted testimony. Now that they  are not here  — [when it could be maintained] that if they had been before us, they  might [even] perhaps have admitted to them  — should they be believed? No, said R. Nahman; set the two [witnesses]  against the two [witnesses]  and leave the property  in the possession of its master.  It is analogous to the [case of the] property of a [certain] madman. A [certain] madman sold property. Two [witnesses] came [and] said [that] he sold [the property] when he was insane, and two [witnesses] came and said [that] he sold [the property] when he was sane.  [And] R. Ashi said: Set the two [witnesses]  against the two [witnesses]  and leave the property  in the possession of the madman. And we say [this] only when he has the ownership-right of his forefathers,  but if he has not the ownership-right of his forefathers, we say that he bought [the property] when he was insane and that he sold [It] when he was insane.  — R. Abbahu said: One rebuts  witnesses only in, their presence, but one contradicts them also in their absence. And a rebuttal in their absence — granted that it is not an [effective] rebuttal,  but it is a contradiction. The Master said [above]: 'If there are witnesses that this is their handwriting, or their handwriting came out from another place. [namely] from a document which was contested and was confirmed in court, they are not believed'. [This is only] if it was contested, but not, if it was not contested.  This is a support  for R. Assi, for R. Assi said: A document  is confirmed only from a document, which was contested and was confirmed in Court. The Nehardeans  said: A document is confirmed only from two kethuboth or from two fields,  and [only] when their owners  used  them for three years, and [that] in comfort.  R. Shimi b. Ashi said: And [only] when it is produced by another person,  but not [if it is produced] by himself.  — Why not [if from] under his own hand? Because he may have forged [the signatures of the witnesses].  [If so]. even when produced by another person also, perhaps he went  and saw  and forged?  — So clearly  he cannot fix [it in his mind]. Our Rabbis taught: A person  may write [down] his testimony in  a document  and may, through it,  give evidence even after many years. R. Huna said: Only when he remembers it  by  himself. R. Johanan said: Even if he does not remember it by himself.  Rabbah said: You may infer from [the words of] R. Johanan [that] if two [persons] know evidence  and one of them has forgotten [it], the other one may remind him  [of it]. They asked: [In the case of] himself  — what is [the law]?  — R. Habina said: Even he himself [may do so]. Mar b. R. Ashi, said: He himself [may] not. And the law is: he himself [may] not.