I say, and with God's success: It starts from the last time of Dhuhr until sunset, and what is considered for sunset is the falling of the sun's disk. This is evident in the desert, but in buildings and mountain peaks — meaning their highest points — it is when no ray of it is seen on the edges of the buildings and mountain peaks, and when darkness approaches from the east. Abu Huraira (may Allah be pleased with him) said: "Indeed, the prayer has a beginning and an end. The first time for Dhuhr prayer is when the sun has passed its zenith, and its last time is when the time for Asr begins. The first time for Asr prayer is when its time begins, and its last time is when the sun turns yellow. The first time for Maghrib is when the sun sets, and its last time is when the twilight disappears. The first time for Isha is when the twilight disappears, and its last time is when midnight is reached. The first time for Fajr is when dawn breaks, and its last time is when the sun rises." This is in Sunan al-Tirmidhi 1: 284, and its narrators are the narrators of the group except for Hanad, as mentioned in I'la al-Sunan 2: 10. And Abdullah ibn Rafi', the freed slave of Umm Salama, the wife of the Prophet (peace be upon him), asked Abu Huraira (may Allah be pleased with him) about the time of prayer, and Abu Huraira said: "I will tell you: Pray Dhuhr when your shadow is equal to your length, and Asr when your shadow is twice your length, and Maghrib when the sun sets, and Isha between you and a third of the night, and pray Fajr in the twilight, meaning in the early dawn." This is in Al-Muwatta of Malik 1: 8, and Musannaf of Abdul Razzaq 1: 450, and its chain of narration is authentic as mentioned in I'la al-Sunan 2: 9. And Jabir (may Allah be pleased with him) said: "Gabriel (peace be upon him) came to the Prophet (peace be upon him) when the sun had passed its zenith, and said: 'Stand up, O Muhammad, and pray Dhuhr when the sun has tilted.' Then he stayed until the shadow of a man was equal to him, and came to him for Asr, saying: 'Stand up, O Muhammad, and pray Asr.' Then he stayed until the sun set, and came to him, saying: 'Stand up and pray Maghrib.' So he stood and prayed it when the sun had set completely. Then he stayed until the twilight disappeared and came to him, saying: 'Stand up and pray Isha.' So he stood and prayed it. Then he came to him when dawn was bright in the morning, saying: 'Stand up, O Muhammad, and pray.' So he stood and prayed Fajr. Then he came to him the next day when the shadow of a man was equal to him, saying: 'Stand up, O Muhammad, and pray.' So he prayed Dhuhr. Then he came to him when the shadow of a man was twice his length, saying: 'Stand up, O Muhammad, and pray.' So he prayed Asr. Then he came to him for Maghrib when the sun had set at one time, and did not leave him, saying: 'Stand up and pray.' So he prayed Maghrib. Then he came to him for Isha when a third of the first night had passed, saying: 'Stand up and pray.' So he prayed Isha. Then he came to him for Fajr when it was very bright, saying: 'Stand up and pray.' So he prayed Fajr. He said: 'The time between these two is all valid.'" This is in Sunan al-Nasa'i al-Kubra 1: 471, and Al-Mujtabi 1: 26. See: Umdat al-Ri'aya 1: 147, and Allah knows best.