Yazid bin Abi Malik al-Shami says that Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) sent Yazid bin Abi Sufyan (may Allah be pleased with him) towards Syria as commander of an army, and himself walked on foot with him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18149