Abd al-Rahman bin Sa'd bin Ammar bin Sa'd (Sa'd (may Allah be pleased with him) being the mu'adhdhin of the Messenger of Allah (peace and blessings be upon him)) says: My father narrated to me from his forefathers (may Allah be pleased with them) that when the Prophet (peace and blessings be upon him) delivered a sermon in battle or fighting, he would lean on a bow, and when he delivered the Friday sermon, he would lean on a staff.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجمعة / 5751