Musannaf Ibn Abi Shayba 7:299

Yazid ibn Harun narrated to us, from Abd al-Malik ibn Abi Sulayman, who said: Ata was asked about a man who made an oath upon himself to pray such and such number of rak'ahs in the Mosque of Iliya (Jerusalem). He said: "Let him pray that number in the Sacred Mosque (al-Masjid al-Haram), for it fulfills his oath, and prayer in the Sacred Mosque is better."