Musnad Ahmad 30:1739

Sulayman narrated to us, Isma'il informed us, 'Amr informed me, from 'Abd al-Rahman al-A'raj, from Abu Hurayrah, that the Prophet, peace and blessings of Allah be upon him, said: "Indeed, a vow does not bring near to the son of Adam anything that Allah had not already decreed for him. However, the vow coincides with the decree, and through it, that which the miser did not intend to spend is extracted from the miser."