Narrated by Ahmad ibn Muhammad ibn ‘Isa, from al-Hasan ibn Mahbub, from Ibrahim al-Karkhi, who said: I asked Abu al-Hasan Musa عليه السلام: “When does the time of Dhuhr begin?” Imam عليه السلام said: “When the sun passes the meridian.” I asked: “When does its time end?” Imam عليه السلام said: “After four forearms (aqdam) have passed from its zenith. Verily, the time of Dhuhr is narrow, not like other times.” I asked: “When does the time of ‘Asr begin?” Imam عليه السلام said: “The end of the time of Dhuhr is the beginning of the time of ‘Asr.” I asked: “When does the time of ‘Asr end?” Imam عليه السلام said: “The time of ‘Asr is until the sun sets, and that is in case of an excuse, and it is a form of negligence.” I said to him: “If a man were to pray Dhuhr after four forearms had passed from the sun's zenith, would he be considered, in your view, as not having fulfilled it?” Imam عليه السلام said: “If he did that deliberately to oppose the Sunnah and the prescribed time, it would not be accepted from him, just as if a man were to delay ‘Asr until it is near sunset, deliberately, without excuse, it would not be accepted from him. Verily, the Messenger of Allah سبحانه وتعالى, may Allah سبحانه وتعالى bless him and his family, assigned times for the obligatory prayers and set boundaries for them in his Sunnah for the people. So whoever turns away from one of his obligatory Sunnahs is like one who turns away from the obligations of Allah سبحانه وتعالى, the Exalted.”