Majma al-Zawaid 3140 — Delivering the sermon standing and sitting

Musa bin Talhah narrates: I was present with Sayyiduna Uthman al-Ghani (may Allah be pleased with him); he delivered the sermon standing on the minbar. I was also present with Sayyiduna Mu'awiyah; he delivered the sermon sitting. He said: "I am not unaware of the Sunnah, but my age has advanced, my bones have become weak, and your affairs have become many. So I intended to settle some of your affairs while sitting; then I will stand and take my share of the Sunnah."
Imam al-Tabarani recorded it in al-Mu'jam al-Kabir; its chain contains a narrator, Qays bin al-Rabi', whom Shu'bah and al-Thawri declared thiqah (trustworthy), while others declared him da'if (weak).