Abdullah bin Muhammad bin Aqil narrates that Ali bin al-Husayn (may Allah be pleased with him) sent him to Rubayyi' bint Mu'awwidh (may Allah be pleased with her) to ask her about the (manner of) ablution of the Messenger of Allah (peace and blessings be upon him). She narrated the hadith about the manner of ablution of the Prophet (peace and blessings be upon him), in which it says that he (peace and blessings be upon him) washed his feet. She says: Ibn Abbas (may Allah be pleased with them both) came to me and I narrated the hadith to him, and he said: I find in the Book (the Qur'an) only two washings and two wipings.
If this is authentic, it is possible that Ibn Abbas (may Allah be pleased with them both) took the reading to be in the genitive, which requires wiping. When it reached Ibn Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) had warned the one who did not wash them, or who left any part of them (unwashed), Ibn Abbas (may Allah be pleased with them both) then held washing the feet to be obligatory and recited the verse in the accusative. The accusative reading has also been narrated from Ibn Abbas (may Allah be pleased with them both).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 340