(… بِالنَّذْرِ… ) (…vows …): This Arabic word means to obligate yourself to do some more of the obligatory acts that prescribed by Allah (swt). For example, if you vowed to pray a certain number of units of prayer, then it is a vow to do something of the same of what Allah (swt) has legislated, since Allah (swt) has legislated prayer and made it obligatory five times a day. It is said that anyone who vows to do more than the obligatory, then this proves that he has loved and felt the sweetness of the worship. It proves, as well, that this worshipper recognizes the greatness of his/her Lord and that He (swt) deserves to be worshipped by more than what He has obliged. This is Allah’s Mercy towards us, for if He (swt) has obliged us to worship Him as He deserves, no one would have been able to fulfil it. You have a choice to take a vow or not, but if you take it, you should fulfil it.

   (… يُوفُونَ بِالنَّذْرِ ) (They fulfill their vows …): Those believers fulfill their vows that they have obliged themselves to do. The formula of the vowe is to say: ‘I obliged myself, for the sake of Allah (swt), to give charity, to pray, to fast, to perform major or minor Hajj, on condition that Allah (swt), for example, heals my patient or that my absent relative returns’. In case the person vowed to do a sin, then he should not fulfil it. ‘Aisha (may Allah be pleased with her) narrated that the Prophet (saws) said:

“If anyone vows to obey God let him obey Him, but if anyone vows to disobey Him let him not disobey Him.”[1]  

As fulfilling the vow is obligatory, the person should fulfil it on behalf of his father or mother if they died before fulfilling it. Ibn ‘Abbas (may Allah be pleased with him) said:

Sa’d bin Obada Al-Ansari asked the Prophet (saws) about a vow that his mother took before she died, the Prophet (saws) said to him: “Fulfil it on her behalf”.

So, one of the descriptions of the servants of Allah (swt) is that they fulfil their vows.

(  وَيَخَافُونَ يَوْمًا كَانَ شَرُّهُ مُسْتَطِيرًا… ) (…and dread a Day whose evil is widespread): A Day refers to the Day of Judgement. The believers, Allah’s servants, fear this great Day because they are certain that it will come undoubtedly. As Allah (swt) mentions the fear and sorrow of the believers on the Day of Judgement, He (swt) also mentions the fear of the believers.

(  شَرُّهُ مُسْتَطِيرًا… ) (…whose evil is widespread.): Its evil spreads like the fire and the light of the day when it spreads in the sky. On that Day, the fear spreads among the people of the heavens and the earth. It will spread in the heavens, hence, the it will split apart, the stars will scatter, the Angels will be in a panic, the moon and the sun will darken. In the earth, the mountains will be torn apart, the water will go down and everything will be destroyed including the buildings and the trees. So, the evil in that Day will spread in the heavens and the earth.       

[1] Sahih al-Bukhari: Book of Oath and Vows, Chapter of Vows to obey Allah, Hadith No. 6696.