Alasbaat (الاسباط) is the plural of the word sibt (سِبْطٌ). The word sibt is used to describe the descendants who are the chosen and or best of all the other descendants who exist. It does not mean tribe or tribes which, in Arabic, is signified by a specific word which is qabeela (قبيلة). It means that, that someone or a group of people are the special or chosen from a group of descendants or off-spring.
The Prophet (saw) described his two grandsons, Hasan and Hussain, as sibtain (سبطين ) meaning the two best of those who descend from him. They were also his chosen line.
الحسن بن عرفة حدثنا إسماعيل بن عياش عن عبد الله بن عثمان بن خيثم عن سعيد بن
راشد عن يعلى بن مرة قال : قال رسول الله صلى الله عليه و سلم حسين مني وأنا
من حسين أحب الله من أحب حسينا حسين سبط من الأسباط
قال أبو عيسى هذا حديث حسن وإنما نعرفه من حديث عبد الله بن عثمان بن خثيم
وقد رواه غير واحد عن عبد الله بن عثمان بن خيثم
“Hussain is from me and I am from Hussain, Allah loves whoever loves Hussain. Hussain is sibt of those who are of the Alasbaat.” Tirmidhi has graded this narration Hasan (good).
When Allah (swt) mentions Alasbaat he only does so when referring to the Children of Israel m and no other. None of the descendants of Ibrahim m are given this name besides the Children of Israel by Allah (swt).
The name cannot be used as a substitute for Banu Israel because there have been times and continue to be occasions when some of the members of Banu Israel are not behaving in a righteous way and therefore they cannot be described as the best descendant. Allah (swt) uses this name to signify the Children of Israel m who are obedient to Him and His messengers which He has sent in their time. An example of when Allah (swt) uses the term is in surah Al Araf 160:
وَقَطَّعْنَاهُمُ اثْنَتَيْ عَشْرَةَ أَسْبَاطًا أُمَمًا ۚ وَأَوْحَيْنَا إِلَىٰ مُوسَىٰ إِذِ اسْتَسْقَاهُ قَوْمُهُ أَنِ اضْرِب بِّعَصَاكَ الْحَجَرَ ۖ فَانبَجَسَتْ مِنْهُ اثْنَتَا عَشْرَةَ عَيْنًا ۖ قَدْ عَلِمَ كُلُّ أُنَاسٍ مَّشْرَبَهُمْ ۚ وَظَلَّلْنَا عَلَيْهِمُ الْغَمَامَ وَأَنزَلْنَا عَلَيْهِمُ الْمَنَّ وَالسَّلْوَىٰ ۖ كُلُوا مِن طَيِّبَاتِ مَا رَزَقْنَاكُمْ ۚ وَمَا ظَلَمُونَا وَلَٰكِن كَانُوا أَنفُسَهُمْ يَظْلِمُونَ
“And We divided them into twelve of the best descendants [as distinct] nations. And We inspired to Moses when his people implored him for water, “Strike with your staff the stone,” and there gushed forth from it twelve springs. Every people knew its watering place. And We shaded them with clouds and sent down upon them manna and quails, [saying], “Eat from the good things with which We have provided you.” And they wronged Us not, but they were [only] wronging themselves.“
As above Allah (swt) has used the term here to describe all of those who were with Musa (as) from Banu Israel. Those that were with him at that time were being obedient to the commands of Allah (swt) and their messenger. When the Children of Israel are not being obedient then Allah (swt) does not use the term Alasbaat as expressed in the same surah at 168:
وَقَطَّعْنَاهُمْ فِي الْأَرْضِ أُمَمًا ۖ مِّنْهُمُ الصَّالِحُونَ وَمِنْهُمْ دُونَ ذَٰلِكَ ۖ وَبَلَوْنَاهُم بِالْحَسَنَاتِ وَالسَّيِّئَاتِ لَعَلَّهُمْ يَرْجِعُونَ
“And We divided them throughout the earth into nations. Of them some were righteous, and of them some were otherwise. And We tested them with good [times] and bad that perhaps they would return”
In this ayah Allah (swt) mentions the Children of Israel and how he divided them in the Earth but this time he does not refer to them as Alasbaat, the rest of the ayah indicates why the esteemed title of Alasbaat is not used. In this Ayah it hints that some will be righteous and others will be less than that therefore, they will not, as a complete group deserve the title of the best descendants. But, those who are righteous will be referred to as Alasbaat. The real difference between those Children of Israel m and the others who are not addressed as Alasbaat is the obedience to the prophet in their time.
This is further expressed in the Quran in surah Saad where Allah (swt) makes it very clear that the line of Ibrahim, Ishaaq and Yacoub is the chosen of the best. This is quite significant as in this statement Allah (swt) deliberately leaves out Ismaeel n who is the older brother of Ishaaq m and is always mentioned before his brother Ishaaq when the family is mentioned except in regards the granting of responsibility and the covenants.
“واذْكُرْ عِبَادَنَا إِبْرَاهِيْمَ وَ إِسْهَاقَ وَ يَعْقُوْبَ أُوْلَي الأَيْدِي وَ الأَبْصَر إنَّا أَخْلَصْنَاهُمْ بِخَالِصَةٍ ذِكْرِيَ الدَّارِ وإِنَّهُمْ عِنْدَنَا لَمِنَ الْمُصْطَفَيْنَ الأَخْيَارِ وَ اذْكُرْ إِسْمَاعِيْلَ وَ الْيَسَعَ وَ ذا الكفْلِ وَ كُلٌّ مِّنَ الْأَخْيَارِ”
“And, remember our slaves Ibrahim and Ishaq and Yacoub foremost in authority and foresight of reality. Indeed, we selected them in the affair of remembering and reminding others in the affair of the house. (either the haram or Jennah or both). And, indeed they with Allah definitely from the chosen of the best and remember Ismaeel and ilyasaa and Dhul kifl and all are from the best.” The members of Banu Israel who are following the Prophet g and striving to implement the sunnah and, most importantly fulfilling their covenant are named Alasbaat. Individually they are called sibt or sibta.