It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him): I was sitting with the Messenger of Allah (peace and blessings be upon him). A man said: O Messenger of Allah, what is your view about praying on the leather called fira'? The Messenger of Allah (peace and blessings be upon him) said: "Then what is tanning for?" (That is, one may pray on it after it has been tanned.)
(b) The first chain is more likely to be the preserved one. Ibn Abi Layla is kathir al-wahm (makes many errors).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 88