Sayyiduna Anas (may Allah be pleased with him) said that when the Messenger of Allah (peace and blessings be upon him) intended to combine Zuhr and Asr on a journey, he would delay Zuhr until the beginning of the time of Asr.
Shababah added some words: then he would combine them.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5522