Ata' bin Abi Rabah (may Allah have mercy on him) narrates: Ibn al-Zubayr (may Allah be pleased with him) led the people in the Maghrib prayer and gave the salam after two rak'ahs. Then he stood up to go to the Black Stone to touch it. He looked back and saw that the people were still seated. Ata' bin Abi Rabah (may Allah have mercy on him) said: He came back and led us in the remaining rak'ah, then gave the salam and performed two prostrations. Ata' said: I went straight away to Ibn Abbas (may Allah be pleased with him) and asked him about it, and he said: Tell me more, may your father be blessed! How did he do it? I repeated it to him, and he said: He did not deviate from the Sunnah of his Prophet (peace and blessings be upon him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3915