Sayyiduna Abu Humayd al-Sa'idi (may Allah be pleased with him) said: I travelled with the Messenger of Allah (peace and blessings be upon him) to Tabuk. He mentioned the hadith, in which it was that the king of Aylah gave the Prophet (peace and blessings be upon him) a white mule as a gift, so the Prophet (peace and blessings be upon him) clothed him with a cloak and wrote a document for him concerning their sea (that is, their territory).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجزية / 18790