Abdullah bin Sulayman bin Abi Zaynab (may Allah have mercy on him) related that Sayyiduna Malik bin Abdullah al-Juhani (may Allah be pleased with him) passed by Sayyiduna Habib bin Maslamah (may Allah be pleased with him) - or Habib bin Maslamah passed by Malik - while he was leading his horse and walking on foot. He said to him: Will you not ride, when Allah has given you a mount? He said: The Messenger of Allah (peace and blessings be upon him) said: "Whoever's feet become dusty in the path of Allah, Allah has made him forbidden to the Fire."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 16711