Muwatta Imam Malik Book of Hajj, Hadith 8

Yahya related to me from Malik from Nafi from Abdullah ibn Umar that a man once asked the Messenger of Allah ﷺ what clothes someone in ihram could wear, and the Messenger of Allah ﷺ said, "Do not wear shirts, turbans, trousers, burnouses, or leather socks, except if you cannot find sandals. In that case you can wear leather socks, but cut them off below the ankles. Do not wear any clothes that have been touched by saffron or yellow dye."
Yahya said that Malik was asked about the hadith attributed to the Prophet ﷺ "Whoever cannot find a waist wrapper should wear trousers," and he said, "I have never heard this, and I do not think that some one who is in ihram can wear trousers, because among the things which the Prophet ﷺ forbade some one in ihram to wear were trousers, and he did not make any exception for them although he did make an exception for leather socks."
20.4 Wearing Clothes when in Ihram

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّ رَجُلاً، سَأَلَ رَسُولَ اللَّهِ ﷺ مَا يَلْبَسُ الْمُحْرِمُ مِنَ الثِّيَابِ فَقَالَ رَسُولُ اللَّهِ ﷺ " لاَ تَلْبَسُوا الْقُمُصَ وَلاَ الْعَمَائِمَ وَلاَ السَّرَاوِيلاَتِ وَلاَ الْبَرَانِسَ وَلاَ الْخِفَافَ إِلاَّ أَحَدٌ لاَ يَجِدُ نَعْلَيْنِ فَلْيَلْبَسْ خُفَّيْنِ وَلْيَقْطَعْهُمَا أَسْفَلَ مِنَ الْكَعْبَيْنِ وَلاَ تَلْبَسُوا مِنَ الثِّيَابِ شَيْئًا مَسَّهُ الزَّعْفَرَانُ وَلاَ الْوَرْسُ .