Can the seller swear by Allah in business transactions?
To emphasize the principle of honesty in business transactions, Allah revealed a verse in the Qur’an condemning the use of false oaths in business transactions.
Abdullah Ibn Aufa or Ibn Abi Aufa said that a man displayed some goods in the market and swore by Allah that he had been offered a price for it which was not offered, and he said this in order to cheat one of the Muslims. It was on this occasion that the following verse was revealed,
“Indeed, those who exchange the covenant of Allah and their [own] oaths for a small price will have no share in the Hereafter,...” 
It was common then and it is common now that people swear by Allah in the course of selling. I found it in many places, so when you go to buy some goods, the price they offer you is 10 riyals or 5 riyals a kilo. The man tells you, ‘by Allah I only bought it for 4 and half riyals! I am only making half a riyal on this kilo.’ In this way, they are lying to the people, as they really bought it for just 2 riyals, but they are swearing by Allah  that they bought it for 4 and half riyals so you know that they have to charge you this half a riyal.
This method in sale has been condemned by Allah, and Allah says that the people who practice this will have no portion in the Hereafter, and the people in such a society will be put in Hell. This doesn’t mean that this act alone will carry one to hell. What happens is this becomes one’s way of life, because this expression in the market ends up being expressed in your other dealings- with your family, your friends etc. and it does not stop there. Thus, you are a liar in the market and outside as well. Lying all the time becomes your habit.
Prophet Mohammed (ﷺ) has said:
“Indeed, truth leads to virtue and virtue leads to Paradise, and a truthful person continues to speak the truth until he becomes the most truthful person. Lies lead to evil and evil leads to Hell, and a liar continues to lie until he is listed as a high ranking liar before Allah." 
We have been discouraged from using any kind of oath in the sale transaction, but it’s not forbidden as long as one is certain that when he swears by Allah, he is telling the truth. We know it is so easy for us to swear by Allah and be lying at the same time, and this is why we have been advised not to use oaths when selling.
Prophet Muhammed (ﷺ) said,
"The swearing (by the seller) may persuade the buyer to purchase the goods but that will be deprived of Allah's blessing.” 
People swear to convince the person of the truth of what they are saying but in doing so they deprive the sale of Allah’s blessings.
 [Qur'an 3:77]
 Imam Ahmad recorded that Abu Dharr said, "The Messenger of Allah said, There are three persons whom Allah will not speak to, look at on the Day of Resurrection or purify, and they shall taste a painful torment. I said, `O Messenger of Allah! Who are they, may they gain failure and loss' He said, repeating this statement thrice, `The Musbil (man whose clothes reach below the ankles), he who swears while lying so as to sell his merchandize and the one who gives charity and reminds people of it')'' This was also recorded by Imaam Bukhari, Book 94, Hadith 7298, and the collectors of the Sunan
 [Bukhari, Book 8, Volume 73, Hadith 116]
 [Bukhari, Volume 3, Book 34, Number 300]< Back to Questions