The father of Abu Bakr bin Abi Musa al-Ash'ari (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him) that a questioner came to him (peace and blessings be upon him) and asked him about the times of prayer. He (peace and blessings be upon him) gave him no answer. He (peace and blessings be upon him) ordered Sayyiduna Bilal (may Allah be pleased with him), and he called the iqamah for Fajr when the dawn broke, while the people could hardly recognise one another. Then he (peace and blessings be upon him) gave the order and the iqamah for Zuhr was called when the sun had declined, while someone was saying: It is midday; yet he (peace and blessings be upon him) knew better than them. And he (peace and blessings be upon him) gave the order, and he called the iqamah for Asr while the sun was high. Then he (peace and blessings be upon him) gave the order, and he called the iqamah for Maghrib when the sun had set. Then he (peace and blessings be upon him) gave the order, and he called the iqamah for Isha when the redness of twilight had disappeared. Then the next day he (peace and blessings be upon him) delayed Fajr until, when he (peace and blessings be upon him) finished, someone was saying: The sun has risen, or nearly so. Then (he prayed) Zuhr when it was close to Asr. Then he (peace and blessings be upon him) delayed Asr until, when he (peace and blessings be upon him) finished, someone was saying: The sun has turned red. Then he (peace and blessings be upon him) delayed Maghrib until the redness of twilight was about to disappear; then he delayed Isha until it was the first third of the night. Then in the morning he (peace and blessings be upon him) called the questioner and said: "The time of prayer is between these two."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1731