The following is taken from Islamtoday.com, but I have taken the liberty of correcting some spelling errors and adding commments in double brackets:
Question: Can you kindly list some Islamic documents concerning either hadîth or Islamic Law, that are extant and that predate the Muwatta’ of Imam Mâlik?
Answered by Sheikh Muhammad al-Qannâs
The Companions of the Prophet (peace be upon him) used to collect all the sayings and actions of the Prophet (peace be upon him) and relate them among themselves and memorise them.
Some of the Companions used to keep written records during the era of the Prophet (peace be upon him). Writings from this time period include the document of Abû Bakr al-Siddîq regarding Zakâh, the document of `Ali b. Abî Tâlib discussing the age classifications of camels and something about injury compensation, and the document authored by `Abd Allah b. `Amr b, al-`Âs entitled al-Sahîfah al-Sâdiqah.
[[My Comment: This Sahîfah contained all the hadîths that `Abd Allâh b. `Amr wrote down from the Prophet (صلى الله عليه وسلم). It is known that he was the most prolific of all the Companions in writing down hadîths. For more, see here.]]
The Successors followed in their footsteps. They relied upon memorization and narration, and some of them recorded some of the Sunnah in writing.
That is why there were some hadîth works written at this time, most notably those of Sa`îd b. Jubayr, Mujâhid b. Jabr (both students of Ibn `Abbâs), Bashîr b. Nuhayk who wrote from Abû Hurayra, Abû al-Zubayr Muhammad b. Muslim b. Tadrus al-Makkî the student of Jâbir b. `Abd Allah, and Hishâm b. `Urwah b. al-Zubayr, in addition to many others that were related from the Successors. These are the second source, after the documents of the Companions themselves, for what was authored afterwards.
At the beginning of the second century of the Islamic Era, the comprehensive recording of the Sunnah went into full swing, due to the fear that the Sunnah could be lost. The first people to do this was Abû Bakr b. Muhammad b. Hazm (d. 120 AH) and Ibn Shihâb al-Zuhrî (d. 124 AH).
In the era immediately following that of the Successors, the Muslims started authoring works in the Sunnah. Scholars collected in these works the hadîth of the Prophet (peace be upon him) and the sayings of the Companions.
Some of the most notable scholars who did so were as follows:
Abû Muhammad `Abd al-Malik b. Jurayj (d. 150 AH) in Mecca
Ma`mar b. Râshid (d.153 AH) in Yemen
Abû `Amr `Abd al-Rahmân b. `Amr al-Awzâ`î (d. 156 AH) in Syria
Sa`îd b. Abî `Arûbah (d. 156 AH)
al-Rabî` b. Subayh (d. 160 AH)
Hammâd b. Salamah (d. 176 AH) in Basra
Muhammad b. Ishâq (d.151 AH)
Sufyân al-Thawrî (d. in 161 AH) in Kufah
al-Layth b. Sa`d (d. 175 AH) in Egypt
Most of these writings have not reached us. However, the hadîth and narrations that they contained were incorporated into the books that were authored afterwards, such as the Musannaf of `Abd al-Razzâq al-San`ânî (d. 211 AH), the Musnad of Ahmad b. Hanbal (d. 241 AH), the Musannaf of Ibn Abî Shaybah (d. 235 AH), and other books of hadîth.
The Muwatta’ is indeed one of the first books of hadîth to have reached us. It is typical of the books that were written in that period in its form. The hadîth of the Prophet (peace be upon him) are mentioned together with the Companions’ sayings and the legal verdicts of the Successors.
Some of the books and documents from the time of the Successors and those who came immediately after them have reached us. Some of these works were source material for Mâlik for his Muwatta’.
These works exist in manuscript form, though some have been prepared in printed editions. Some of these are:
– al-Hadîth by al-A`mash (d. 148 AH) as narrated by Wakî` (d.148 AH)
– Kitâb al-Manâsik by Ibn Abî `Arubah (d. in 156H)
– A part of al-Sirah by Ibn Ishâq (d. 151H)
– A part of al-Ahâdîth by Ibn Jurayj (d. 150 AH)
– A portion of a manuscript of Ibn Tahmân (d. 168 AH)
– A manuscript of Juwayriyyah related from Nâfi`, the ward of Ibn `Umar, (d. 117 AH)
– A manuscript of `Ubayd Allah b. `Umar related from Nâfi`, the ward of Ibn `Umar, (d. 117 AH)
– A manuscript of Suhayl b. Abî Sâlih (d. 138 AH)
– Part one of the narrations of Sufyân al-Thawrî (d. 161 AH)
– A manuscript of al-Layth b. Sa`d from Yazîd b. Abî Habîb (d. 128 AH).
– A munuscript of Shu`ayb b. Abî Hamzah from al-Zuhrî (d. in 124 AH).
[References: Dirâsât fi al-Hadîth al-Nabawî wa Târîkh Tadwînah, by Dr. Muhammad Mustafâ al-A`zumî (2/471-483), Ma`rifat al-Nusakh wal Suhuf al-Hadîthiyyah by Bakr b. `Abd Allah Abû Zayd and Târîkh al-Turâth al-`Arabî by Fu’âd Zaskîn (1/117)]
Regarding the books of Islamic Law which were authored before the Muwatta’, it is known that the beginning of the Islamic Law took the form of the legal verdicts made by the Companions and the Successors, like those known as “the Seven Jurists” as well as others.
Most all of their legal verdicts can be found in the books of the Sunnah and the commentary of the Qur’ân. A good number of them are mentioned in the Muwatta’.
Some short treatises and small books have been discovered, such as al-Farâ’id by Zayd b. Thâbit [[This is of particular note as Zayd b. Thâbit is a Companion!]] and al-Tafsîr by Abî al-Zinâd (d. 131 AH).
[Refer to: Fu’âd Zaskîn, Târîkh al-Turâth al-`Arabî (3/15-16)]
May Allah guide us all.