Musnad Ahmad 1153:1769

Waki’ and ‘Abd al-Rahman narrated to us—the meaning being the same—from Sufyan, from al-Miqdam ibn Shurayh, from his father, from ‘Aishah, who said: "Whoever tells you that the Messenger of Allah (peace and blessings of Allah be upon him) urinated while standing after the Furqan (the Quran) was revealed to him, do not believe him. He did not urinate while standing since the Furqan was revealed to him." ‘Abd al-Rahman said in his narration: "The Messenger of Allah (peace and blessings of Allah be upon him) did not urinate while standing since the Furqan was revealed to him."