The majority of what is known from his life comes from the book Asrar al-Tawhid اسرارالتوحید(The Mysteries of Unification ) by Mohammad Ibn Monavvar one of his grandsons, written 130 years after his death.
The book, which is an important early Sufi writing in Persian, presents a record of his life in the form of anecdotes from a variety of sources and contains a collection of his words. He was born in the village Mihne, a part of the Persian province of Greater Khorasan, today this village is located in Turkmenistan near the Iranian border. His father was a herbalist and physician with an interest in Sufism.
Abusaeid’s formal education included Islamic scholarship and Arabic literature that he continued until the age 23 when he left them for Sufism. During his life his fame spread throughout the Islamic world, even to Spain. He was the first Sufi writer to widely use ordinary love poems as way to express and illuminate mysticism, and as such he played a major role in foundation of Persian Sufi poetry. He spent most of his life in Neishabour.
His mysticism is a typical example of the Khorasani school of Sufism. He extracted the essence of the teachings of the past Sufis of this school (and to some extent other schools as well) and expressed them in a simpler, and in a sense deeper, form without the use of philosophy.
He held a special reverence for earlier Sufis, especially Bayazid Bastami and Hallaj. Moreover, in Asrar al-Tawhid, Tazkiratul Awliyā and Noorul Uloom it has been written that Shaikh Abusaïd went for the visit of Shaikh Abul Hassan Kharaqani and got deeply influenced by his personality and state.
His system is based on a few themes that appear frequently in his words, generally in the form of simple emotional poems.
The main focus of his teachings is liberation from “I” , which he considered the one and only cause of separation from God and to which he attributed all personal and social misfortunes. His biography mentions that he would never call himself "I" or "we" but “they” instead. This idea of selflessness appears as Fotovvat (a concept very near to chivalry) in his ethical teachings and as Malaamat, a kind of selflessness before the Beloved which he considers a sign of perfect love in his strictly mystical teachings.
Both of these concepts in a certain sense are spiritual forms of warrior ethics. Despite their simplicity he believed that the full application of these teachings to one's life requires both divine grace and the guidance of an experienced Sufi, and is impossible through personal efforts alone. His picture as portrayed in various Sufi writings is a particularly joyful one of continuous ecstasy. Other famous Sufis made frequent references to him, a notable example being the Persian Sufi poet Farid al-Din Attar, who mentions Abusaeid as his spiritual guide. Many miracles are attributed to him in Sufi writings.
A few sayings of Abusaeid quoted from his biography Asrar al-Tawhid :
Many short Persian poems are attributed to him and he is considered one of the great medieval Persian poets. The attribution of these poems has always been doubtful and due to recent research, it is generally believed that he wrote only two poems in his life. The attribution of so many poems to Abusaeid was due to his great fondness for poetry. His love for poetry can be seen from the fact that he usually used love poetry written by non-Sufis in his daily prayers. Even his last words were a poem, and at his funeral instead of the recitation of Qur’anic verses, he requested the following poem.
Another example of the poems attributed to him.
Abusaeid insists that his teachings and Sufism as a whole are the true meaning of Islam. He based his teachings on the mystic interpretation of verses from Qur’an and some hadiths and was considered a learned Islamic scholar. Nevertheless his interpretations of Qur’an were different from the mainstream Islamic thought of the time.
Also at his time the Islamic legitimacy of Sufi dance was a matter of debate among the scholars and some attempted to try him and his followers on charges of un-Islamic innovations, dancing and use of poetry in public sermons, but they failed to do so because of his popularity. Similar legal troubles had dogged other Sufis, notably Farid al-Din Attar and al-Hallaj.
Another important fact is that he never fulfilled the pilgrimage to Kaaba, called Hajj, which according to all schools of Islamic jurisprudence is one of the five pillars of Islam and an obligation upon all Muslims. In his biography Asrar al-Tawhid, he writes: “God knows – and this word is worth a hundred oaths – that everyone for whom God opened the way of pilgrimage to Kaaba, was already rejected by him from the path of truth.”
To this day this has been one of the causes of criticizing him from a religious point of view. In general he was bold in expressing his mystic opinions as can be seen from his praise of Hallaj who was considered a heretic by most of the Sufis and all of the non-Sufi Muslims of the time, although the common opinion about Hallaj changed in time.
There is evidence that Abusaeid and Avicenna, the famous Persian physician and philosopher, corresponded with one another. Abusaeid records several meetings between them in his biography. The first meeting is described as three days of private conversation, at the end of which Abusaeid said to his followers that everything that he could see (i.e in visions), Avicenna knew, and in turn Avicenna said that everything he knew Abusaeid could see.