It was narrated from 'Ubaydullah bin Ka'b: "I heard my father Ka'b bin Malik narrate: 'I said: O Messenger of Allah, Allah, the Mighty and Sublime, has saved me by my being truthful, and as part of my repentance I want to give my wealth in charity to Allah and His Messenger. He said: Keep some of your wealth for yourself; that is better for you. I said: I will keep my share that is in Khaibar.'"
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا مُحَمَّدُ بْنُ مَعْدَانَ بْنِ عِيسَى، قَالَ حَدَّثَنَا الْحَسَنُ بْنُ أَعْيَنَ، قَالَ حَدَّثَنَا مَعْقِلٌ، عَنِ الزُّهْرِيِّ، قَالَ أَخْبَرَنِي عَبْدُ الرَّحْمَنِ بْنُ عَبْدِ اللَّهِ بْنِ كَعْبٍ، عَنْ عَمِّهِ، عُبَيْدِ اللَّهِ بْنِ كَعْبٍ قَالَ سَمِعْتُ أَبِي كَعْبَ بْنَ مَالِكٍ، يُحَدِّثُ قَالَ قُلْتُ يَا رَسُولَ اللَّهِ إِنَّ اللَّهَ عَزَّ وَجَلَّ إِنَّمَا نَجَّانِي بِالصِّدْقِ وَإِنَّ مِنْ تَوْبَتِي أَنْ أَنْخَلِعَ مِنْ مَالِي صَدَقَةً إِلَى اللَّهِ وَإِلَى رَسُولِهِ . فَقَالَ " أَمْسِكْ عَلَيْكَ بَعْضَ مَالِكَ فَهُوَ خَيْرٌ لَكَ " . قُلْتُ فَإِنِّي أُمْسِكُ سَهْمِي الَّذِي بِخَيْبَرَ .
sunnah.com