Do not take vows, for a vow has no effect against Fate; it is only from the miserly that something is extracted. (Using translation from Muslim 1640a)  

أَنَّ رَسُولَ اللهِ ﷺ قَالَ «لَا تُنْذِرُوا فَإِنَّ النَّذْرَ لَا يُغْنِي مِنَ الْقَدَرِ شَيْئًا وَإِنَّمَا يُسْتَخْرَجُ بِهِ مِنَ الْبَخِيلِ»