Musannaf Ibn Abi Shayba 7:279

Hammad bin Khalid al-Khayyat narrated to us, from Muhammad bin Hilal, who heard Sa’id bin al-Musayyib saying: Whoever says, "It is upon me to walk to the House of Allah," then it is nothing, unless he says, "It is a vow upon me to walk to the Ka'bah."