مُوَطَّأُ مَالِكٍ
Muwatta Malik 719
Hajj
حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، كَانَ يَكْرَهُ لُبْسَ الْمِنْطَقَةِ لِلْمُحْرِمِ .
Yahya related to me from Malik from Nafi that 'Abdullah ibn 'Umar used to disapprove of anybody wearing a belt or girdle while in ihram.
Arabic/English book reference: Book 20, Hadith 12