That the Messenger of Allah ﷺ said: "Do not vow, for the vows does not prevent what is decreed at all, and it only causes the miser to spend (of his wealth)."  

قَالَ رَسُولُ اللَّهِ ﷺ لاَ تَنْذِرُوا فَإِنَّ النَّذْرَ لاَ يُغْنِي مِنَ الْقَدَرِ شَيْئًا وَإِنَّمَا يُسْتَخْرَجُ بِهِ مِنَ الْبَخِيلِ قَالَ وَفِي الْبَابِ عَنِ ابْنِ عُمَرَ