Musa bin Salamah says that I asked Sayyiduna Ibn Abbas (may Allah be pleased with them both), "If I go to Makkah Mukarramah, how should I perform the prayer?" He replied: "Two rak'ahs, and this is the Sunnah of Abul Qasim (peace and blessings be upon him)."
Hadith Referenceمسند احمد / ومن مسند بني هاشم / 2632