Sayyiduna Sahl bin Abi Hathmah (may Allah be pleased with him) said — he was the chief of his people — that Sayyiduna Abdullah bin Sahl and Sayyiduna Muhayyisah (may Allah be pleased with them both) went out to Khaybar. Then he narrated the complete hadith about the killing of Abdullah, including that the Prophet (peace and blessings be upon him) had said: "Take the oath and become entitled to the blood of your companion."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب القسامة / 16455