Musannaf Ibn Abi Shayba 7:287

12431. Abd al-Rahim narrated to us, from Abdullah ibn Sa'id, from his grandfather, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Beware of making vows (nadhr), for Allah does not bestow a favor because of a vow. It is merely a thing by which something is extracted from the miser."