'Abdullah reported that Allah's Messenger (ﷺ) got his head shaved (after slaughtering the sacrificial animal on the 10th of Dhu'l-Hijja), and so did a group of Companions, while some of them got their hair clipped. Abdullah said:Allah's Messenger (may peace'be upon him) observed once or twice:" May Allah have mercy upon those who get their heads shaved." And he also said:" Upon those too who got their hair clipped."
وَحَدَّثَنَا يَحْيَى بْنُ يَحْيَى، وَمُحَمَّدُ بْنُ رُمْحٍ، قَالاَ أَخْبَرَنَا اللَّيْثُ، ح وَحَدَّثَنَا قُتَيْبَةُ، حَدَّثَنَا لَيْثٌ، عَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ، قَالَ حَلَقَ رَسُولُ اللَّهِ صلى الله عليه وسلم وَحَلَقَ طَائِفَةٌ مِنْ أَصْحَابِهِ وَقَصَّرَ بَعْضُهُمْ . قَالَ عَبْدُ اللَّهِ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " رَحِمَ اللَّهُ الْمُحَلِّقِينَ - مَرَّةً أَوْ مَرَّتَيْنِ ثُمَّ قَالَ - وَالْمُقَصِّرِينَ " .
Muslim
The Book of Pilgrimage • Hadith 348