Chapter on the Prayer Times (Mawaqit)

And from him, from Muhammad ibn Abi Hamzah and Husayn ibn Hashim and Ibn Ribat and Safwan ibn Yahya, all from Ya‘qub ibn Shu‘ayb from Abu Abdillah عليه السلام, who said: I asked Imam عليه السلام about the time of Dhuhr prayer. Imam عليه السلام said: “When the shadow is the length of one arm's span (dhira‘).”