Musnad Ahmad 30:2217

'Affan narrated to us, 'Abd al-Rahman ibn Ibrahim narrated to us, al-'Ala' narrated to us, from his father, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Do not make vows, for the vow does not bring forward anything of the decree, and it is only a means by which something is extracted from the miser."