[Purchasing a Commodity Whose Price Increase You Learned of Before the Seller Knew]

The answer—and by Allah’s enabling: That is permissible and valid, due to His saying, “And Allah has permitted trade and forbidden usury,” [Al-Baqarah:275] and His saying, “...except that it be trade by mutual consent among you.” [An-Nisā’:29]
Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2