Sahih al-Bukhari — One-fifth of Booty to the Cause of Allah (Khumus) — Hadith No: 3125
Translation
Narrated Aslam:`Umar said, "Were it not for those Muslims who have not come to existence yet, I would have distributed (the land of) every town I conquer among the fighters as the Prophet (ﷺ) distributed the land of Khaibar