Isma'il narrates from Amir al-Sha'bi that he was asked about a man who had vowed to walk to the House of Allah; he walked half the way and then rode. Ibn Abbas (may Allah be pleased with him) said: Next year he should ride as much as he walked, and walk as much as he rode, and sacrifice a camel.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النذور / 20130