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

Ibn Abbas reported that Mu'awiya had said to them:

Do you know that I clipped some hair from the head of Allah's Messenger (ﷺ) at al- Marwa with the help of a clipper? I said: I do not know it except as it verdict against you.

حَدَّثَنَا عَمْرٌو النَّاقِدُ، حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ، عَنْ هِشَامِ بْنِ حُجَيْرٍ، عَنْ طَاوُسٍ، قَالَ قَالَ ابْنُ عَبَّاسٍ قَالَ لِي مُعَاوِيَةُ أَعَلِمْتَ أَنِّي قَصَّرْتُ مِنْ رَأْسِ رَسُولِ اللَّهِ صلى الله عليه وسلم عِنْدَ الْمَرْوَةِ بِمِشْقَصٍ فَقُلْتُ لَهُ لاَ أَعْلَمُ هَذَا إِلاَّ حُجَّةً عَلَيْكَ ‏.‏

Ibn Abbis (Allah be pleased with him) reported that Mu'awiya b. Abu Safyin had told him:

I clipped the hair (from the head of) Allah's Messenger (ﷺ) with a clipper while he was at al-Marwa, or I saw him getting his hair clipped with a clipper as he was at al-Marwa. 1722

وَحَدَّثَنِي مُحَمَّدُ بْنُ حَاتِمٍ، حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، عَنِ ابْنِ جُرَيْجٍ، حَدَّثَنِي الْحَسَنُ، بْنُ مُسْلِمٍ عَنْ طَاوُسٍ، عَنِ ابْنِ عَبَّاسٍ، أَنَّ مُعَاوِيَةَ بْنَ أَبِي سُفْيَانَ، أَخْبَرَهُ قَالَ قَصَّرْتُ عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم بِمِشْقَصٍ وَهُوَ عَلَى الْمَرْوَةِ أَوْ رَأَيْتُهُ يُقَصَّرُ عَنْهُ بِمِشْقَصٍ وَهُوَ عَلَى الْمَرْوَةِ ‏.‏

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 Umra except one who had brought the sacrificial animal with him. When it was the day of Tarwiya (8th of Dhul-Hijja) and we went to Mini, we (again) pronounced Talbiya for Hajj.

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 يَوْمُ التَّرْوِيَةِ وَرُحْنَا إِلَى مِنًى أَهْلَلْنَا بِالْحَجِّ ‏.‏

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.

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 ‏.‏

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 women), whereupon jibir said: We have been doing this during the lifetime of Allah's Messenger (ﷺ), and then 'Umar forbade us to do so, and we never resorted to them.

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 فَلَمْ نَعُدْ لَهُمَا ‏.