قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ : " لا يَأْتِي ابْنَ آدَمَ النَّذْرُ بِشَيْءٍ لَمْ أَكُنْ قَدْ قَدَّرْتُهُ، وَلَكِنَّهُ يُلْفِيهِ النَّذْرُ وَقَدْ قَدَّرْتُهُ لَهُ أَسْتَخْرِجُ بِهِ مِنَ الْبَخِيلِ، وَيُؤْتِينِي عَلَيْهِ مَا لَمْ يَكُنْ آتَانِي مِنْ قَبْلُ "
And the Messenger of Allah, peace and blessings be upon him, said: “(Allah the Exalted says) The vow of the son of Adam does not give him anything except what I have already written in his destiny. Rather, the vow brings him to that which I have decreed for him. Through it, I extract wealth from the miser, and because of the vow, he gives Me as much as he could not have given Me before making the vow.”
Related hadith on this topic