Sa’d ibn Ubaida reported: A man came to Ibn Abbas and he said, “Is there repentance for one who kills a believer?” Ibn Abbas said, “No, there is nothing but Hellfire.” After the man left, those sitting nearby said to him, “What is this? You have given us two different judgments, for earlier you judged that whoever killed a believer may have his repentance accepted. What is the matter today?” Ibn Abbas said, “Indeed, I suspect he was an angry man intending to kill a believer.” Later they followed the man and found that it was true.
Source: Musannaf Ibn Abi Shayba 27182, Grade: Sahih (authentic) according to Ibn Hajar
Sufyan At-Thawri said, “When the scholars were asked if there is repentance for murder, they would say no. If a man had already committed it, they would command him to repent.”
Source: At-Talkhees Al-Habir 2574
عَنْ سَعْدِ بْنِ عُبَيْدَةَ قَالَ جَاءَ رَجُلٌ إلَى ابْنِ عَبَّاسٍ فَقَالَ لِمَنْ قَتَلَ مُؤْمِنًا تَوْبَةٌ قَالَ لَا إلَّا النَّارُ فَلَمَّا ذَهَبَ قَالَ لَهُ جُلَسَاؤُهُ مَا هَكَذَا كُنْتَ تُفْتِينَا كُنْتَ تُفْتِينَا أَنَّ لِمَنْ قَتَلَ مُؤْمِنًا تَوْبَةً مَقْبُولَةً فَمَا بَالُ هَذَا الْيَوْمِ قَالَ إنِّي أَحْسِبُهُ رَجُلا مُغْضَبًا يُرِيدُ أَنْ يَقْتُلَ مُؤْمِنًا قَالَ فَبَعَثُوا فِي أَثَرِهِ فَوَجَدُوهُ كَذَلِكَ
27182 مصنف ابن أبي شيبة كتاب الديات من قال للقاتل توبة
المحدث ابن حجر العسقلاني خلاصة حكم المحدث رجاله ثقات
قَالَ سُفْيَانُ كَانَ أَهْلُ الْعِلْمِ إِذَا سُئِلُوا قَالُوا لَا تَوْبَةَ لَهُ فَإِذَا ابْتُلِيَ رَجُلٌ قَالُوا لَهُ تُبْ
2574 التلخيص الحبير في تخريج أحاديث الرافعي الكبير كتاب القضاء
Source: Daily Hadith