Muwatta Malik (Yahya)

It is narrated from Abdullah bin Abi Habibah that I said to a person, and I was young at the time, that if someone only says «عَلَيَّ مَشْيٌ إِلَى بَيْتِ اللّٰهِ» meaning, "It is upon me to walk to the House of Allah," and does not say, "It is a vow upon me to walk to the House of Allah," then nothing becomes obligatory upon him. That person said to me, "I have this cucumber in my hand, I give it to you, so just say, 'It is upon me to walk to the House of Allah.'" I said, "Yes, I will say it," so I said it, and I was young. Then, after a short while, I came to my senses and people said to me that walking to the House of Allah has become obligatory upon you. I went to Sa'id bin al-Musayyib and asked him, and he also said that walking to the House of Allah has become obligatory upon you, so I walked to the House of Allah.
Imam Malik, may Allah have mercy on him, said: This is the ruling according to us.