Muwatta' Malik 1011

Yahya related to me from Malik that Abdullah ibn Abi Habiba said, "I said to a man, when I was young, 'A man who only says that he must walk to the House of Allah and does not say that he has vowed to walk, does not have to walk.' A man said, 'Shall I give you this small cucumber?' and he had a small cucumber in his hand and you will say, 'I must walk to the house of Allah?' I said, 'Yes' and I said it, for at that time I was still immature. Then, when I came of age, some one said to me that I had to fulfill my vow. I went and asked Said ibn al- Musayyab about it, and he said to me, 'You must walk.' So I walked." Malik said, "That is the custom among us