It is sad that many people today do not know what Ahlul-Bayt are, although their unique position in the Muslim's faith is foundational! Ahlul-Bayt (special members of the Household) are the main notables of the Household of the Messenger of Allah, Sayyiduna Muhammad, Blessings be upon him and his Ablul-Bayt, who is the Head of this holy Household, while Ali in Abi Talib is the father and Master of the blessed progeny that emanated from them. The Holy Messenger mentioned them by name, Fatima, Ali, Hasan and Husain and the Imams from their offspring, as stated in several Hadiths by the Holy Messenger. Every Imam of them played a crucial role in introducing and preserving the original genuine Message of the Holy Messenger, even by offering their own souls in this holy cause. They never committed a wrong nor a sin. They were models and masters of virtue and benevolence. They stood against evil and corruption, and taught people true faith in God, beautiful manners, selflessness and modesty. The Holy Quran testified to their magnificence, perfection and purity. These are known as Ahlul-kisaa and Ahlul-'abaa (members of the Mantle), who are the closest relatives in spiritual status to the Holy Messenger and have more rights over the Muslims than any other relatives. In the Holy Quran, Allah Almighty has established the vital principle of having love for them and loyalty to them, as in Surat al-Shura, as well as their right to receiving al-fai' (gains from the enemy without fighting), as in Surat al-Hashr, and al-khoms (fifth of the war booty), as in Surat al-Anfal. The extended concept of Ahlul-Bayt also includes all male relatives of the Holy Messenger from the progeny of Bani Hashim and Bani al-Muttalib.
Source: Sage Lion of God by Hazrat Shaykh Sayyid Dr. Alsharif Shamsuddin Alhusaini (damat barakatuhum)
The people of Allah do not lead the same spiritual life like that of the ordinary people. The people of Allah search for the Divine Secrets in His creation. They follow the hearts in which Allah Almighty manifests Himself with His Majesty and Beauty - the Master of creation, Muhammad, Blessings be upon him and his family; his Vicegerent, Ali ibn Abi Talib, Blessings be upon him; the Chief of all women, Fatima Az-Zahra, Blessings be upon her; the Perfumes of Paradise: Al-Hasan and Al-Husain and the Awliya of their family Ahlul-Bayt, Blessings be upon them, and of the loyal Companions of the Prophet Blessings be upon him, Allah be pleased with them.
If it was not for the fact that Allah has preserved the religion through our Mawla Master Imam Ali ibn Abi Talib (Blessings be upon him), who has extended the Muhammadi lights and the sacred knowledge to the Sheikhs of the Sufi Paths, the Divine Secrets would have disappeared forever after the departure of Sayyiduna Muhammad Blessings be upon him and his Ahlul-Bayt.
Hadrat Ibn Abbas said, the Messenger of Allah (Blessings be upon him and his Ahlul-Bayt) said: "Love Allah for He is the Source of all bounties, and love me for His love for me, and love my Ahlul Bayt (family and descendants) for my love for them".
(Al-Tirmizi and Al-Bukhari)
Hadrat Abu Saeed Alkhudri said, the Messenger of Allah (Blessings be upon him and his Ahlul-Bayt) said: "By Allah Who holds my soul, anyone who hates us Ahlul Bayt will definitely enter the Fire of Hell".
(Sahih by Al-Hakim and Ibn Hibban).
Some issues of the Islam that was prevented from reaching the Sunnis today:
Conveying of Salam and Salawat to Ahlul Bayt of the Prophet, Blessings be upon him and his family, stopped long ago, and was replaced with the term "radiya Allahu anhu/ anha" (Allah be pleased with him/her), and by so doing fell the distinction of Ahlul Bayt, Blessings be upon them, and became just equal to the other righteous people!
After the early elders of the Sunnis used to say "Ali ibn Abi Talib alaihis salam" and "Fatima Az-Zahra alaihas salam" and "Hasan and Husain alaihim assalam", many scholars, for various reasons, followed the approach of the Nasibis (haters/jealous of Ahlul Bayt) and began writing "radiya Allahu anhu" instead!
I encourage all Muslims to revive the Sunnah of the early notable Alwliya of Allah of the first two centuries, and say with every name of Ahlul-Bayt: "alaihis salam/alaihas salam" (Blessings be upon him/ Blessings be upon her). Stop saying "Allah be pleased with him/her," which is supposed to be used for the righteous of lesser status of the Companions and the Alwliya who are not from Ahlul Bayt. This is the glorious arrangement of Allah Almighty and His Messenger Blessings be upon him and his Ahlul-Bayt.
Sahih Muslim, hadith 5955:
A'isha reported that the Prophet (salla Allahu alayhi wa aalihi wasallam) went out one morning wearing a striped cloak of black camel's hair, then there came Al Hasan ibn 'Ali (alaihis-salam). He sheltered Alhasan with it, then came Al Husain and he sheltered him with it along with Hasan. Then came Fatima and he took her under it, then came 'Ali and he also took him under it, and then said: "Allah truly desires to take away any impurities from you, O members of the Household, and to purify you with perfect purification".
Sahih Muslim, hadith 5951:
Abu Huraira reported Allah's Messenger (sallAllaahu alayhi wa sallam) as saying to Hasan: O Allah, behold, I love him. You too love him and love the one who loves him.
Sahih Bukhari, Volume 5, Book 57, Number 89:
I heard the Prophet talking at the pulpit while Al-Hasan was sitting beside him. The Prophet would look at the people once and look at Al-Hasan once, and say, "This son of mine is a Sayid (chief) and Allah may bring about an agreement between two groups of Muslims through him."
Sahih Bukari, Volume 5, Book 57, Number 92:
I saw the Prophet carrying Al-Hasan on his shoulder an saying, "O Allah! I love him, so please love him."
Sahih Bukhari, Volume 5, Book 57, Number 96:
A person asked 'Abdullah ibn 'Umar whether a Muslim could kill flies. I heard him saying (in reply). "The people of Iraq are asking about the killing of flies while they themselves murdered the son of the daughter of Allah's Apostle!! The Prophet pbuh said, "in this world, Hasan and Husain are my two sweet smelling flowers."
Sahih Bukhari, Volume 5, Book 57, Number 51:
Allah's Apostle said, "Tomorrow, I will give the Army flag to a man with whose leadership Allah will grant (the Muslims) victory." So the people kept on thinking the whole night as to who would be given the flag. The next morning the people went to Allah's Apostle and every one of them hoped that he would be given the flag. The Prophet pbuh asked, "Where is Ali ibn Abi Talib?" The people replied, "He is suffering from eye illness, O Allah's Apostle." He said, "Send for him and bring him to me." So when 'Ali came, the Prophet spat in his eyes and invoked blessings on him, and he was immediately cured as if he had no ailment. The Prophet pbuh then gave Ali the flag.."
Sahih Tirmizi,
Book 49, Hadith 4078
The Prophet (ﷺ) said: "For whomever I am his Mawla (master and ally) then 'Ali is also his Mawla (master and ally)."
Musnad Ahmad ibn Hanbal:
Hadhrat Abu Zharr (Radhi Allahu Anhu) while holding the Door of the Ka'ba, said that he had heard the Holy prophet (Salla Allahu alaihi wasallam) say, "My Ahlul Bayt among you are like Noah's Ark. He who boards it will be safe, but he who holds back from it will perish."
Sahih Tirmizi:
Hadrat Zaid ibn Arqam (Radhiya Allahu 'Anhu) said Allah's Messenger (Salla Allahu alaihi wasallam) said of Ali, Fatima, al-Hasan and al-Husain, "I am war with one who makes war on them and I am peace to one who has peace with them."