Sahih Muslim , Book 15, Hadith 348 (In-Book) ⓘ

'Abdullah reported that Allah's Messenger 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 ‏" ‏ ‏.‏