Urwah bin Udhaynah narrated that I set out (for Hajj) with my grandmother; she had vowed to walk to the House of Allah. But along the way, she became unable (to continue walking). So I asked Abdullah bin Umar (may Allah be pleased with them both) about the matter, and Abdullah bin Umar (may Allah be pleased with them both) said: "Tell her to ride, then walk, and whenever she becomes unable, let her ride." Imam Malik (may Allah have mercy on him) said: "And a sacrifice is obligatory upon her."
Hadith Referenceمسند الإمام الشافعي / كتاب النذور / 1042
Hadith Takhrijاسناده صحیح اخرجه البيهقي : 81/10 ۔ وفي المعرفة السنن والآثار له (5843) ۔ ومالك في الموطأ، الندور ، باب ما جاء فى من نذر شيئًا الى بيت الله۔