Jabir said he intended to go to Khaibar, so he went to the Prophet, gave him a salutation and told him of his purpose. He replied, “When you come to my agent take fifteen camel-loads from him, and if he desires a sign from you put your hand on his collar-bone*”. *This was evidently a pre-arranged sign to show that the Messenger was genuine. Abu Dawud transmitted it.
Hadith Referenceمشكوة المصابيح / كتاب البيوع / 2935
Hadith Gradingالألبانی:ضَعِيف | زبیر علی زئی:إسناده ضعيف
Hadith Takhrij´تحقيق و تخريج: محدث العصر حافظ زبير على زئي رحمه الله` «إسناده ضعيف، رواه أبو داود (3632) ٭ محمد بن إسحاق بن يسار مدلس و لم أجد تصريح سماعه .»