It is narrated from Sayyiduna Usamah bin Zayd (may Allah be pleased with him) that he set off with the Prophet (peace and blessings be upon him) on the evening of Arafah, and he (peace and blessings be upon him) turned off into the valley and relieved himself. Sayyiduna Usamah (may Allah be pleased with him) began pouring water for him (peace and blessings be upon him) while he (peace and blessings be upon him) performed ablution. Sayyiduna Usamah (may Allah be pleased with him) said to him (peace and blessings be upon him): "O Messenger of Allah (peace and blessings be upon him), will you (peace and blessings be upon him) not pray?" He (peace and blessings be upon him) said: "The prayer is ahead of you (i.e., the time of the prayer is still ahead)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 390