It is permissible for the pilgrim performing Umrah to shorten his hair and he does not have to shave it. It is recommended for him to shave his hair or shorten it at Al-Marwah

Sahih Muslim · Book 15 · Hadith 1247

حَدَّثَنِي عُبَيْدُ اللَّهِ بْنُ عُمَرَ الْقَوَارِيرِيُّ، حَدَّثَنَا عَبْدُ الأَعْلَى بْنُ عَبْدِ الأَعْلَى، حَدَّثَنَا دَاوُدُ، عَنْ أَبِي نَضْرَةَ، عَنْ أَبِي سَعِيدٍ، قَالَ خَرَجْنَا مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم نَصْرُخُ بِالْحَجِّ صُرَاخًا فَلَمَّا قَدِمْنَا مَكَّةَ أَمَرَنَا أَنْ نَجْعَلَهَا عُمْرَةً إِلاَّ مَنْ سَاقَ الْهَدْىَ فَلَمَّا كَانَ…

Abu Sa'id (Allah be pleased with him) reported: We went out with Allah's messenger (ﷺ) pronouncing loudly the Talbiya for Hajj When we came to Mecca, he commanded us that we should change this (Ihram for Hajj) to that of…

Sahih Muslim · Book 15 · Hadith 1248

وَحَدَّثَنَا حَجَّاجُ بْنُ الشَّاعِرِ، حَدَّثَنَا مُعَلَّى بْنُ أَسَدٍ، حَدَّثَنَا وُهَيْبُ بْنُ خَالِدٍ، عَنْ دَاوُدَ، عَنْ أَبِي نَضْرَةَ، عَنْ جَابِرٍ، وَعَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، - رضى الله عنهما - قَالاَ قَدِمْنَا مَعَ النَّبِيِّ صلى الله عليه وسلم وَنَحْنُ نَصْرُخُ بِالْحَجِّ صُرَاخًا ‏.‏

jibir and Abil Salld al-Khudri (Allah be pleased with them) reported: We went with Allah's Messenger (ﷺ) and we were pronouncing Talbiya for Hajj loudly.

Sahih Muslim · Book 15 · Hadith 1249

حَدَّثَنِي حَامِدُ بْنُ عُمَرَ الْبَكْرَاوِيُّ، حَدَّثَنَا عَبْدُ الْوَاحِدِ، عَنْ عَاصِمٍ، عَنْ أَبِي نَضْرَةَ، قَالَ كُنْتُ عِنْدَ جَابِرِ بْنِ عَبْدِ اللَّهِ فَأَتَاهُ آتٍ فَقَالَ إِنَّ ابْنَ عَبَّاسٍ وَابْنَ الزُّبَيْرِ اخْتَلَفَا فِي الْمُتْعَتَيْنِ فَقَالَ جَابِرٌ فَعَلْنَاهُمَا مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم ثُمَّ نَهَانَا عَنْهُمَا عُمَرُ فَ…

Abd Nadra reported: While I was in the company of Jibir, a person came and said: There is difference of opinion amomg Ibn Abbas and Ibn Zubair about two Mut'as (benefits, Tamattul in Hajj and temporary marriage with wome…