Imam al-Shafi'i (may Allah have mercy on him) said: "If he is able to walk, walking is binding upon him."
Our companions said: "Because walking to a place of righteousness is (in itself) righteousness." This is by inference from the saying of Allah Almighty: "They will come to you on foot." [Surah al-Hajj: 27]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النذور / Q20105