The Prophet ﷺ said, "If a pilgrim in ihram cannot find sandals, let him wear leather socks, but let him cut them below the ankles."
حدثنا هشيم أخبرنا ابن عون عن نافع
أن النبي ﷺ قال إذا لم يجد المحرم النعلين فليلبس الخفين وليقطعهما أسفل من الكعبين
Its isnad is sahih, and it is an abridgment of a hadith that will come at 4482. Malik reported it in Muwatta 1:303 from Ibn Umar. The authors of the six books also reported it, as noted in Muntaqa 2432.