It is narrated from Urwah bin Udhaynah Al-Laithi that he said: I set out with my grandmother, and she had made a vow to go to the House of Allah on foot. She became tired on the way, so she sent her slave to ask Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) about the issue, and I also went with him. He asked Sayyiduna Abdullah bin Umar (may Allah be pleased with them both), and he replied: Now she should ride, and then when she returns, she should walk from the place where she started riding.
Imam Malik (may Allah have mercy on him) said: And despite this, a sacrificial animal (hady) is also obligatory upon her.

Saeed bin Musayyib and Abu Salamah bin Abdur Rahman used to say regarding this issue as was said by Sayyiduna Abdullah bin Umar (may Allah be pleased with them both).

Yahya ibn Sa'id said: I had made a vow to walk to the House of Allah, but I developed pain in my navel, so I rode to Mecca and asked 'Ata ibn Abi Rabah and others. They said: You are required to offer a sacrificial animal (hady). When I came to Madinah, I asked the people there, and they said: You must walk again from the place where you mounted (your ride). So I walked.

Imam Malik, may Allah have mercy on him, said: In our view, if a person says that he must walk to the House of Allah, and he starts walking but then becomes unable, he may ride. Then, when he returns again, he should walk from the place where he had started riding. If he does not have the strength to walk, then he should walk as far as he is able, then ride, and for the hady he should offer a camel or a cow; if he is unable, then a goat.

Imam Malik (may Allah have mercy on him) was asked: If a person says to someone, "I will carry you to the House of Allah (the Ka'bah)," what is the ruling? Imam Malik (may Allah have mercy on him) replied: If his intention was that he would carry him on his own neck and by saying this he only meant to put himself in hardship, then in this case it is not obligatory upon him; rather, he should walk on foot and offer a sacrificial animal. And if he did not intend anything specific, then he should perform Hajj riding and also take that person with him for Hajj, because he said, "I will carry you to the House of Allah." However, if that person refuses to go with him, then nothing is obligatory upon him, because he has fulfilled his obligation.

Imam Malik (may Allah have mercy on him) was asked: If a person makes several vows that are impossible to fulfill in his entire lifetime, for example, "I will go to the House of Allah on foot," or "I will not speak to my father or brother," is it sufficient for him to fulfill one vow, or is it necessary to fulfill all the vows? Imam Malik (may Allah have mercy on him) replied: In my view, it is necessary to fulfill all the vows as much as possible and for as long as possible, and to seek closeness to Allah, Glorious and Exalted is He, through good deeds as much as one is able.