Sayyiduna Abdullah bin Abi al-Hamsa (may Allah be pleased with him) said: I made a transaction with the Messenger of Allah (peace and blessings be upon him) before his (peace and blessings be upon him) prophethood. Then he mentioned a hadith with the same meaning.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20836