The Prophet had started teaching the message of Islam and had made many enemies. As a result, some of the unbelievers began to make fun of him at the death of his sons, calling him "Abtar"...
Lady Fatimah Zahra (SA) was born to lady Khadija (SA) and the Prophet . Before her birth, the Prophet had two sons, Qasim and Tahir, but both boys had died when they were babies.
The Prophet had started teaching the message of Islam and had made many enemies. As a result, some of the unbelievers began to make fun of him at the death of his sons, calling him "Abtar".[1]
The word Abtar means a creature that has no tail - and was meant to say that the Prophet was tail-less because he had no children to carry on his family.Thus, when Bibi Fatimah (SA) was born, the following Sura of the Holy Qur'an was revealed:
"In the Name of Allah, the most Kind, the most Merciful. Verily (O Muhammad),We have given you Kauthar. So pray to your Lord and give sacrifice. Verily, your enemies will be Abtar." [2]
The revelation of this Surah was, in fact, an answer to the enemies of the Apostle to inform them that the descendants of the prophet and Islam and the Qur'an would remain and ceaselessly continue, forever.
When the Holy Prophet (Peace and Blessings be upon him) was asked what Kauthar meant, he replied that it was a stream in heaven and the man who would give water from that stream to the believers was Imam Ali (AS) .[3][4]
Kauthar also meant abundance, and the birth of lady Fatimah (SA) signified that,because as mentioned, this verse was revealed when some of the unbelievers insulted the prophet by calling him abtar, but the prophet was not abtar, because through Lady Fatima, his descendants would be in abundance.[5]
Ibn abi al-Hadid mentions a hadith in his commentary on Nahj al-Balagha that Amr ibn As asked Imam Ali that why he was regarding Hassan and Hussayn as descendants of the prophet and Imam Ali replied, because if they were not the descendants of the prophet, he would be Abtar but God has called his enemy as Abtar not him because he was given Koutharr, so Kouthar is Fatima and his descendants.
The promise of Allah was certainly true because today, there are countless descendants of the prophet while the enemies of the Holy Prophet were those who became truly "Abtar".
So this chapter of the holy Quran is a reference to lady Fatima.
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[1] NOOR AL-thAQALAYN. V 5. P 684. 684.
دَخلَ رسولُ اللّه المسجدَ وفیه عمرُو بنُ العاص والحکمُ بن أبی العاص، فقال عمرو: یا أبا الأبتر! و کان الرجلُ فی الجاهلیة إذا لم یکن له ولدء سُمِّیَ أبترَ، ثمّ قال عمرو: إنّی لأشنأ محمَّداً أی اُبغِضُه، فأنزل اللّهُ علی رسوله(ص): «إِنّا أَعْطَیْناک الْکَوْثَرَ ء فَصَلِّ لِرَبَّک وَانْحَرْ ء إِنَّ شانِئَک ـ أی مُبغِضَک عمرو بنُ العاص ـ هُوَ الأََبْتَرُ».
[2] [08:-3]
بِسْمِ اللَّـهِ الرَّ‌حْمَـٰنِ الرَّ‌حِيمِ إِنَّا أَعْطَيْنَاكَ الْكَوْثَرَ ﴿١﴾ فَصَلِّ لِرَ‌بِّكَ وَانْحَرْ ﴿٢﴾ إِنَّ شَانِئَكَ هُوَ الْأَبْتَر
[3] Al-durul-manthur. V 6. P 401
قال: هَل تَدرونَ مَا الکَوثَرُ؟ قالوا: اللّهُ و رسولُه أعلم، قال: هو نهرء أعطانیه ربّی فی الجَنَّة علیه خیرء کثیرء تَرِدُه أُمَّتی یومَ القِیامةِ آنِیَتُه عَدَدُ الکَواکِبِ یَختَلِجُ العَبدُ منهم، فأقول: یا ربِّ! إنَّه مِن اُمَّتی، فیُقالُ: إنَّک لا تَدری ما أحدَثَ بعدَک.
[4] Yanabi al-mavadah. P 132.
فى المناقب ان رسول الله صلى الله عليه و آله قال: اعطيت فى على خمس، هن احب الى من الدنيا و ما فيها الى ان قال و اما الثالثة فهو واقف على حوضى يسقى من عرفه من امتى
[5] As some commentators have commented on it as being the 'abundance of the descendants' all of whom came from his daughter, Fatimah Zahra (as), and they multiplied to such an extent that it is impossible to count them. To read more, you can refer to Tafsir al-Mizan.