I intended to set out for Khaybar, so I came to the Messenger of Allah ﷺ, greeted him, and said to him, "I intend to travel to Khaybar."He said, "When you come to my agent, take fifteen wasqs from him. If he asks you for a sign, place your hand on his collarbone."
أردت الخروج إلى خيبر، فأتيت رسول الله ﷺ، فسلمت عليه، وقلت له: إني أردت الخروج إلى خيبر، فقال: إذا أتيت وكيلي فخذ منه خمسة عشر وسقا، فإن ابتغى منك آية فضع يدك على ترقوته.
Abu Dawud (3632) narrated it, and Bayhaqi (6/80) and Daraqutni (4/154) transmitted it from him, from Ubaydullah bin Saad bin Ibrahim, who said, my uncle told us, my father told us, from Abu Ishaq, from Abu Naeem Wahb bin Kaysan, from Jabir bin Abdullah, and he related it.Its chain of transmission is sahih. The uncle of Ubaydullah bin Saad is Yaqub bin Ibrahim, and his father is Ibrahim bin Saad bin Ibrahim, and both are reliable.As for his statement, "on his collarbone," with the ta pronounced with a fatha, it refers to the bone that lies between the hollow of the throat and the shoulder. There are two collarbones, one on each side.