Musnad Ahmad 30:880

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, I heard al-‘Ala’ narrating from his father, from Abu Hurayrah, from the Prophet (peace and blessings of Allah be upon him): That he forbade vowing, and he said: "It does not avert anything of the decree, but it is only a means by which something is extracted from the stingy person."