Sayyidah Umm Salamah (may Allah be pleased with her) said that the Messenger of Allah (peace and blessings be upon him) said: "Tanning makes the skin of a dead animal lawful just as wine becomes lawful when it turns into vinegar." Faraj said: That is, when wine changes and becomes vinegar, it becomes lawful. Faraj bin Fadalah alone narrated it from Yahya, and he is da'if (weak); he narrates from Yahya bin Sa'id a number of hadiths in which he is not corroborated. This was said by Abu al-Hasan al-Daraqutni (may Allah have mercy on him). On this interpretation the disagreement disappears, except that the hadith is weak.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الرهن / 11202