What is the ruling on one who says, "I swear by Allah, my profit on this shirt is 5 riyals," when his profit is much more than that?

The ruling on this type of oath is حرمة (prohibition/sacred inviolability), based on the Prophet's (peace be upon him) saying: "There are three whom Allah will not speak to on the Day of Resurrection, nor will He look at them, nor will He purify them, and for them is a painful torment: The Musbil (one who lets his garment hang below the ankles), the Mannan (one who reminds others of his favors), and the seller who disposes of his goods by a false oath." This is a yameen ghamoos (a deeply sinful oath) that plunges its maker into sin or Hellfire. Its definition among scholars is: "An oath sworn falsely, knowingly, and intentionally concerning a matter." Scholars have differed regarding the necessity of expiation for it. The majority of scholars hold that expiation is not obligatory, because it is among the major sins, whose sin is too great to be expiated by a kaffarat yameen (oath expiation), and therefore, one must repent and seek forgiveness. Imam Shafi'i, however, held that expiation is obligatory for it.