He—may Allah have mercy on him—was asked about wine:

“If it turns into vinegar without his knowledge, may he consume it or sell it? And if he knows that it has turned into vinegar, may he consume some of it or sell it?”

He replied:

As for deliberately turning wine into vinegar, there is disagreement. Some hold that this is permissible, as is reported from Abū Hanīfa. Others hold that it is not permissible, but that if it is turned into vinegar, it becomes pure, as is reported from Mālik. Another view permits doing so by moving it from sunlight into shade, uncovering it, or similar means, without adding anything to it. This is one opinion within the schools of al-Shāfi'ī and Ahmad.

Others hold that deliberately turning it into vinegar is impermissible under any circumstances. This is the position of some followers of al-Shāfi'ī and Ahmad, and it is the correct view. For it is established that the Prophet—peace and blessings be upon him—

“was asked about wine belonging to orphans, and he ordered that it be poured away. He was told, ‘They are poor,’ and he replied, ‘Allah will enrich them out of His bounty.’”

Since he ordered that it be poured away and forbade turning it into vinegar, he must be obeyed in what he commanded and prohibited. Wine must therefore be poured away, not turned into vinegar. This was despite their being orphans and despite that wine having been made before the prohibition, so they had committed no sin.