(a) It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the time of Zuhr lasts until Asr, that of Asr until Maghrib, that of Maghrib until Isha, and that of Isha until Fajr.
(b) Sayyiduna Ibn Abbas (may Allah be pleased with them both) said concerning the time of Zuhr: The time of the Zuhr prayer is from the declining of the sun until the Asr prayer; whenever within that time you pray, you have caught it.
(c) And the meaning that Imam al-Shafi'i (may Allah have mercy on him) described is also established from the Sunnah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1711