Hadith 507190
Chapter 20: Hajj - كتاب الحج
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.
Reference Muwatta Malik 507190
USC-MSA web (English) reference : Book 20, Hadith 12