It was narrated from Abu Moosa that he used to advise people to do Tamattu` (in Hajj). A man said to him: Do not rush in giving fatwas, for you do not know what Ameer al-Mu`mineen has decided with regard to Haji. When he met him later on, he asked him and ‘Umar said: I know that the Prophet (ﷺ) did it and his Companions did it, but I do not like to have intercourse with beneath the arak trees and go out to Hajj with their heads dripping(from ghusl).
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا أَبُو عَبْدِ اللَّهِ، مُحَمَّدُ بْنُ جَعْفَرٍ حَدَّثَنَا شُعْبَةُ، عَنِ الْحَكَمِ، عَنْ عُمَارَةَ بْنِ عُمَيْرٍ، عَنْ إِبْرَاهِيمَ بْنِ أَبِي مُوسَى، عَنْ أَبِي مُوسَى، أَنَّهُ كَانَ يُفْتِي بِالْمُتْعَةِ فَقَالَ لَهُ رَجُلٌ رُوَيْدَكَ بِبَعْضِ فُتْيَاكَ فَإِنَّكَ لَا تَدْرِي مَا أَحْدَثَ أَمِيرُ الْمُؤْمِنِينَ فِي النُّسُكِ بَعْدَكَ حَتَّى لَقِيَهُ بَعْدُ فَسَأَلَهُ فَقَالَ عُمَرُ رَضِيَ اللَّهُ عَنْهُ قَدْ عَلِمْتُ أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَدْ فَعَلَهُ وَأَصْحَابُهُ وَلَكِنِّي كَرِهْتُ أَنْ يَظَلُّوا بِهِنَّ مُعَرِّسِينَ فِي الْأَرَاكِ وَيَرُوحُوا لِلْحَجِّ تَقْطُرُ رُءُوسُهُمْ.
sunnah.com