[Hastening to Purchase the Commodity Before the Seller Knows Its Price Has Risen]

The answer—and Allah is the granter of success: The sale and purchase mentioned are valid—this is what is apparent—because it is a sale arising from mutual consent. However, it is not fitting for a believer to engage in it, in light of what faith entails of sincere counsel and loving good for the believers, and because that may engender rancor in the hearts of the sellers toward the buyer who seized the opportunity of their ignorance of the price increase.
If it be said: Why do you not also declare it a prohibited sale?
We say: We did not say so because the sale was by the consent and choice of both seller and buyer; thus it is a valid sale. Allah Most High has said: “And Allah has permitted sale and forbidden usury.” [Al-Baqarah:275] Hence, such a sale is lawful by the explicit text of this verse.
Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2