Yahya related to me from Malik that he had heard that Jabir ibn Abdullah al-Ansari was asked about wiping over a turban. He said, "Not unless you have wiped over your hair with water."

وَحَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ جَابِرَ بْنَ عَبْدِ اللَّهِ الأَنْصَارِيَّ، سُئِلَ عَنِ الْمَسْحِ، عَلَى الْعِمَامَةِ فَقَالَ لاَ حَتَّى يُمْسَحَ الشَّعْرُ بِالْمَاءِ ‏.‏
USC-MSA web (English) reference : Book 2, Hadith 39
Arabic reference : Book 2, Hadith 69