Sayyiduna Mihjan (may Allah be pleased with him) said: I prayed Zuhr - or Asr - in my house, then I came to the Prophet (peace and blessings be upon him) and sat with him. Then the prayer was established; the Prophet (peace and blessings be upon him) prayed and I did not pray. When he finished, he said: "Are you not a Muslim?" I said: "Of course." He (peace and blessings be upon him) said: "Then why did you not pray?" I said: "I have already prayed in my house." The Prophet (peace and blessings be upon him) said: "When the prayer is established, pray, even if you have already prayed."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17830