Reference for Ketubot 55:7

איכא דאמרי לא אוקי רבא שליח בינתייהו א"ל רב אדא בר מתנא ניקום מר שלוחא בינתייהו א"ל והא [אמר] רב נחמן תנא באבל רבתי כו' א"ל ה"מ היכא דלא גייסי בהדדי אבל הני קא חזינא להו דגייסי בהדדי:

There are those who say: Rava did not place a messenger between them. R. Adda b. Matanah said to him: Let the Master place a messenger between them. He answered him: Did not R. Nahman say: “It is taught in Evel Rabbati, etc.”? He said to him: This refers to a case where they are not familiar with one another, but [as to] these, I see that they are familiar with one another.

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