Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
tabarani:8926 – ʿAlī b. ʿAbd al-ʿAzīz > Abū Nuʿaym > al-Masʿūdī > al-Qāsim b. ʿAbd al-Raḥman > ʿAbdullāh b. Masʿūd Taʿallamūā al-Farāʾiḍ Faʾinnah Yūshik

[Machine] "That a man becomes impoverished of the knowledge he used to possess or remains among people who do not possess it."  

الطبراني:٨٩٢٦ – حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ الْعَزِيزِ ثنا أَبُو نُعَيْمٍ ثنا الْمَسْعُودِيُّ عَنِ الْقَاسِمِ بْنِ عَبْدِ الرَّحْمَنِ قَالَ قَالَ عَبْدُ اللهِ بْنُ مَسْعُودٍ «§تَعَلَّمُوا الْفَرَائِضَ فَإِنَّهُ يُوشِكُ

أَنْ يَفْتَقِرَ الرَّجُلُ إِلَى عِلْمٍ كَانَ يَعْلَمُهُ أَوْ يَبْقَى فِي قَوْمٍ لَا يَعْلَمُونَ»  

See similar narrations below:

Collected by Dārimī
darimi:2895 – Abū Nuʿaym > al-Masʿūdī > al-Qāsim > ʿAbdullāh Taʿallamūā al-Qurān And al-Farāʾiḍ Faʾinnah Yūshik

[Machine] "Abdullah said, 'Learn the Quran and the religious obligations, for soon a person may become in need of knowledge that he once knew or be surrounded by a people who are ignorant.'"  

الدارمي:٢٨٩٥ – حَدَّثَنَا أَبُو نُعَيْمٍ حَدَّثَنَا الْمَسْعُودِيُّ عَنْ الْقَاسِمِ قَالَ قَالَ

عَبْدُ اللَّهِ «تَعَلَّمُوا الْقُرْآنَ وَالْفَرَائِضَ فَإِنَّهُ يُوشِكُ أَنْ يَفْتَقِرَ الرَّجُلُ إِلَى عِلْمٍ كَانَ يَعْلَمُهُ أَوْ يَبْقَى فِي قَوْمٍ لَا يَعْلَمُونَ»