The Messenger of Allah ﷺ said, "Allah says, 'A vow does not bring to the son of Adam anything I have not already decreed for him, but the vow is something I cause him to undertake regarding what I have already decreed for him. Through it I extract something from the miser, so he gives Me on its account what he had not given Me before.'"
قال رسول الله ﷺ: قال الله: لا يأتي ابن آدم النذر بشيء لم أكن قدرته له، ولكنه يلقيه النذر بما قد قدرته له، يستخرج به من البخيل، يؤتيني عليه ما لم يكن آتاني عليه من قبل.
Imam Ahmad (8152) and Ibn Jarud (932) both narrated it from the hadith of Abdul-Razzaq bin Hammam, who said, Mamar narrated to us, from Hammam bin Munabbih, who said, "This is what Abu Hurairah narrated to us," and then he mentioned it. Its isnad is sahih, and it is a hadith qudsi. In some copies of Ahmad's text, "Allah said" is not mentioned, but the wording of the hadith indicates that its presence in other copies is correct.