The so-called hadiths are based on verbal reports, which were in circulation after the death of Mohammed. From the 8th century they were evaluated and collected in large collections to preserve the knowledge of the sunna of the Prophet, and are considered sacred traditions (hadith qudsi).
The traditions were finally grouped together in collections . The most important collections for Shiites are the four books (kutub arbaa). Among the Sunnis, there are the six books (al-kutub as-sitta) important.
== Holy books ==
The quran does not allow other religion in 3:85: ' And whoever desires other than Islam as religion - never will it be accepted from HIM, and he, in the Hereafter, will be among the losers'.
But the Quran mentions earlier revelations in chapter 42(as-Sura) : '...what We enjoined upon Abraham and Moses and Jesus - to establish the religion and not be divided therein'. So there is really no reason for Sunni and Shia Muslims.
The four books mentioned by name in the Quran are the Tawrat revealed to Musa, the Zabur revealed to Dawud, the Injil revealed to Jesus, and the Quran revealed to Muhammad. Other mentioned books are the Scrolls of Abraham (Ṣuḥuf Ibrāhīm), Book of John the Baptist (Kitāb Yaḥyā) and the Scrolls of Moses (Ṣuḥuf Mūsā).
Obviously Mohammed never heared of much higher planes of the divine than Allah(Ishvara), who is only the creator of the lowest spiritual plane - and of the worlds below. This was not relevant at that time because the knowledge of still higher divine worlds does not mean that the souls are allowed to develop so high. Islam teaches that man can only become a friend of Allah - the step 17 of the universal path - and not unite with HIM - the step 19 of the universal path. There are also other heavens or Lokas of the White Brothership and of buddhism.