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
hakim:6306 – Muḥammad b. Ṣāliḥ b. Hāniʾ > Jaʿfar b. Muḥammad b. Sawwār > Qutaybah b. Saʿīd > Jarīr > Sālim b. Abū Ḥafṣah > ʿAbdullāh b. Malīk al-ʿIjlī > Ibn ʿAbbās Qabl Mawtih Bithalāth

[Machine] I heard Ibn Abbas three days before his death saying, "O Allah, I repent to You for the fatwas I used to give to people regarding exchange transactions."  

This is a hadith with an authentic chain of narration. It is among the most noble virtues of Abdullah ibn Abbas that he retracted his fatwa and did not insist upon it.
الحاكم:٦٣٠٦ – حَدَّثَنِي مُحَمَّدُ بْنُ صَالِحِ بْنِ هَانِئٍ ثَنَا جَعْفَرُ بْنُ مُحَمَّدِ بْنِ سَوَّارٍ ثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ أَنْبَأَ جَرِيرٌ عَنْ سَالِمِ بْنِ أَبِي حَفْصَةَ عَنْ عَبْدِ اللَّهِ بْنِ مَلِيكٍ الْعِجْلِيِّ قَالَ

سَمِعْتُ ابْنَ عَبَّاسٍ قَبْلَ مَوْتِهِ بِثَلَاثٍ يَقُولُ «اللَّهُمَّ إِنِّي أَتُوبُ إِلَيْكَ مِمَّا كُنْتُ أُفْتِي النَّاسَ فِي الصَّرْفِ»  

هَذَا حَدِيثٌ صَحِيحُ الْإِسْنَادِ وَهُوَ مِنْ أَجَلِّ مَنَاقِبِ عَبْدِ اللَّهِ بْنِ عَبَّاسٍ أَنَّهُ رَجَعَ عَنْ فَتْوَى لَمْ يَنْقِمْ عَلَيْهِ فِي شَيْءٍ غَيْرَهَا صحيح