Hadith record

Hadith.653 – Zurarah asked Imam Muhammad ibn Ali Al-Baqir (as) about the timing of the Dhuhr (noon) prayer. Imam (as) replied: "It is one arm's length (shadow) from the sun's decline, and the time for Asr (afternoon) is two arm's lengths from the time of Dhuhr, which is four feet from the sun's decline." He then added, "The wall of the Prophet’s Mosque (sw) was as high as a person's stature, and when a shadow reached one arm's length, the Dhuhr prayer would be performed, and when it reached two arm's lengths, the Asr prayer would be performed." He then asked: "Do you know why the measure of one and two arm's lengths was set?" I said: "Why was that made so?" Imam (as) said: "It is for the sake of the supererogatory (nafilah) prayers. You may perform the supererogatory prayers from the sun's decline until the shadow reaches one arm's length; when it reaches one arm's length, you begin the obligatory prayer and leave the supererogatory prayer. When it reaches two arm's lengths, you begin the obligatory prayer and leave the supererogatory prayer."

Translation: Bab Ul Qaim Publications — attributed by Thaqalayn·The Arabic above is the original.