Allah, exalted be His praise, says: "Detain them both after the prayer, then let them both swear by Allah." [Surah al-Ma'idah: 106]
Imam al-Shafi'i (may Allah have mercy on him) said: "And the commentators have said: (It refers to) the Asr prayer."
The Shaykh (Imam al-Bayhaqi) (may Allah have mercy on him) said:
Abu Musa al-Ash'ari (may Allah be pleased with him) said concerning the story of the will: This matter has not happened since the time of the Prophet (peace and blessings be upon him). Then he made the two of them swear after Asr that they had not acted treacherously.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20700