It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that when Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) dispatched Sayyiduna Yazid bin Abi Sufyan (may Allah be pleased with him) (with an army) towards Syria, he himself walked with them on foot for about two miles. It was said to him: O Caliph of the Messenger! Would that you returned now? Sayyiduna Abu Bakr (may Allah be pleased with him) replied: "Certainly not; for I heard the Messenger of Allah (peace and blessings be upon him) say: 'Whoever's feet become dusty in the path of Allah Almighty, Allah, the Mighty and Majestic, will make them both (the feet) forbidden to the Fire of Hell.'"
Imam al-Bazzar narrated this hadith through Amr bin Ali from Abu Nasr al-Tammar as marfu' (attributed to the Prophet).
Hadith Referenceالمطالب العالية بزوائد المسانيد الثمانية / كتاب الجهاد / 1961
Hadith Takhrij«حکم الحدیث المطالب العالیہ محققاً تنسیق د. سعد بن ناصر بن عبد العزيز الشَّثري- مکتبہ شاملہ :حكمه مذكور تحت الحديث المحال إليه. » «أخرجه مسند البزار برقم: 22، وأخرجه المطالب العالية لابن حجر برقم: 1939»