Sayyiduna Abu Rifa'ah al-Adawi (may Allah be pleased with him) said: I came to the Messenger of Allah (peace and blessings be upon him) while he (peace and blessings be upon him) was delivering a sermon, and I said: "O Messenger of Allah, a stranger has come who wants to ask about his religion; he does not know what his religion is." Then the Messenger of Allah (peace and blessings be upon him) came over, leaving his sermon. Then a chair was brought whose legs I thought were of iron, and the Messenger of Allah (peace and blessings be upon him) sat up on it and began teaching me some of what Allah had taught him (peace and blessings be upon him). Then he resumed his sermon and completed it.
Hadith Referenceالمعجم الكبير للطبراني / باب التاء / 1271