It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that when the Messenger of Allah (peace and blessings be upon him) came to Madinah, Sayyiduna Abdullah bin Salam (may Allah be pleased with him) was (busy) up a date palm. Sayyiduna Abdullah bin Salam (may Allah be pleased with him) came to the Messenger of Allah (peace and blessings be upon him) and said: "I want to ask you about some things that no one knows except a prophet; if you answer me about them, I will believe in you." (The narrator then related the full hadith.)
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13961