Radd al-Shams (Arabic: ردّ الشمس; returning of the Sun) is a miracle of the Prophet (s) and one of the indicators of Imam 'Ali (a)'s significant status. In this event, while the sun was setting, the Prophet (s) supplicated to Allah so that the sun returned back and Imam 'Ali (a) had enough time to pray his 'Asr prayer.
In one account, al-Shaykh al-Mufid narrates from Asma' bt. 'Umays, Umm Salama the wife of the Prophet (s), Jabir b. 'Abd Allah al-Ansari, Abu Sa'id al-Khudri and some other companions of the Prophet (s) that: one day, the holy Prophet (s) sent Imam 'Ali (a) for a job and when he returned, it was the time for 'Asr prayer. The Prophet (s) was not aware that Imam 'Ali (a) had not prayed his 'Asr prayer, so he rested while his head was on Imam 'Ali’s leg. At the same time revelation was sent down to the Prophet (s) and it continued until near the sunset. When the Prophet (s) finished receiving the revelation, He asked Imam 'Ali (a) whether or not he had prayed his 'Asr prayer. "Since your blessed head was on my leg and you were resting, I couldn't wake you up." Imam 'Ali (a) responded. The Prophet (s) asked God to return the sun so that Imam 'Ali (a) can pray his 'Asr prayer. In that moment, the sun came back to the extent that it was the proper time for 'Asr prayer and Imam 'Ali (a) performed his 'Asr prayer.