What Bro SyrianFellow said.
SubhanAllah even I didn't know about the sheep. I just knew that Qaabil's sacrifice was rejected, I didn't know what it was. This incident is mentioned in the Qur'an in brief. I also know it was something regarding their wives/marriage as well.
وَاتْلُ عَلَيْهِمْ نَبَأَ ابْنَيْ آدَمَ بِالْحَقِّ إِذْ قَرَّبَا قُرْبَانًا فَتُقُبِّلَ مِنْ أَحَدِهِمَا وَلَمْ يُتَقَبَّلْ مِنَ الْآخَرِ قَالَ لَأَقْتُلَنَّكَ ۖ قَالَ إِنَّمَا يَتَقَبَّلُ اللَّهُ مِنَ الْمُتَّقِينَ
لَئِن بَسَطتَ إِلَيَّ يَدَكَ لِتَقْتُلَنِي مَا أَنَا بِبَاسِطٍ يَدِيَ إِلَيْكَ لِأَقْتُلَكَ ۖ إِنِّي أَخَافُ اللَّهَ رَبَّ الْعَالَمِينَ
إِنِّي أُرِيدُ أَن تَبُوءَ بِإِثْمِي وَإِثْمِكَ فَتَكُونَ مِنْ أَصْحَابِ النَّارِ ۚ وَذَٰلِكَ جَزَاءُ الظَّالِمِينَ
فَطَوَّعَتْ لَهُ نَفْسُهُ قَتْلَ أَخِيهِ فَقَتَلَهُ فَأَصْبَحَ مِنَ الْخَاسِرِينَ
فَبَعَثَ اللَّهُ غُرَابًا يَبْحَثُ فِي الْأَرْضِ لِيُرِيَهُ كَيْفَ يُوَارِي سَوْءَةَ أَخِيهِ ۚ قَالَ يَا وَيْلَتَا أَعَجَزْتُ أَنْ أَكُونَ مِثْلَ هَٰذَا الْغُرَابِ فَأُوَارِيَ سَوْءَةَ أَخِي ۖ فَأَصْبَحَ مِنَ النَّادِمِينَ
Recite to them the truth of the story of the two sons of Adam. Behold! they each presented a sacrifice (to Allah): It was accepted from one, but not from the other. Said the latter: "Be sure I will slay thee." "Surely," said the former, "Allah doth accept of the sacrifice of those who are righteous.
"If thou dost stretch thy hand against me, to slay me, it is not for me to stretch my hand against thee to slay thee: for I do fear Allah, the cherisher of the worlds.
"For me, I intend to let thee draw on thyself my sin as well as thine, for thou wilt be among the companions of the fire, and that is the reward of those who do wrong."
The (selfish) soul of the other led him to the murder of his brother: he murdered him, and became (himself) one of the lost ones.
Then Allah sent a raven, who scratched the ground, to show him how to hide the shame of his brother. "Woe is me!" said he; "Was I not even able to be as this raven, and to hide the shame of my brother?" then he became full of regrets-
Surah # 5 - Al Ma'idah - Verses 27-31