Sayyiduna al-Bara' bin Azib (may Allah be pleased with him) said: I made eighteen journeys with the Prophet (peace and blessings be upon him), and I never saw him (peace and blessings be upon him) leave the two rak'ahs before Zuhr.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5505