Language:
كتاب فرض الخمس
57  
One-fifth of Booty to the Cause of Allah (Khumus)
(19)
Chapter: What the Prophet saws used to give to those Muslims whose faith was not so firm
(19)
بَابُ مَا كَانَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يُعْطِي الْمُؤَلَّفَةَ قُلُوبُهُمْ وَغَيْرَهُمْ مِنَ الْخُمُسِ وَنَحْوِهِ
Sahih al-Bukhari 3146

Narrated Anas:

The Prophet (ﷺ) said, "I give to Quraish people in order to let them adhere to Islam, for they are near to their life of Ignorance (i.e. they have newly embraced Islam and it is still not strong in their hearts."

حَدَّثَنَا أَبُو الْوَلِيدِ، حَدَّثَنَا شُعْبَةُ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ ـ رضى الله عنه ـ قَالَ قَالَ النَّبِيُّ صلى الله عليه وسلم ‏ "‏ إِنِّي أُعْطِي قُرَيْشًا أَتَأَلَّفُهُمْ، لأَنَّهُمْ حَدِيثُ عَهْدٍ بِجَاهِلِيَّةٍ ‏"‏‏.‏
Reference : Sahih al-Bukhari 3146
In-book reference : Book 57, Hadith 54
USC-MSA web (English) reference : Vol. 4, Book 53, Hadith 374
  (deprecated numbering scheme)