Muhammad ibn Ahmad ibn Yahya al-Ash’ari narrated from al-Abbas ibn Ma’ruf, from Safwan ibn Yahya, from Ishaq ibn ‘Ammar, from Isma’il al-Ju’fi, from Abu Ja’far عليه السلام, who said: (Imam عليه السلام said) “The Messenger of Allah سبحانه وتعالى, may Allah سبحانه وتعالى bless him and his family, when the shadow of the wall reached one forearm, He صلى الله عليه وعلى آله وسلم would pray Dhuhr, and when it reached two forearms, He صلى الله عليه وعلى آله وسلم would pray ‘Asr.” I asked: “The walls differ, some are short and some are tall.” Imam عليه السلام said: “The wall of the Prophet’s mosque, may Allah سبحانه وتعالى bless him and his family, at that time was one man's height.”