There has been a lot of reference to the Muwațța being authored due to a command or instruction from one of the Abbasid kings these narrations do not bear well with the scholarly tradition of Madinah. Historically scholarship stayed aloof of politics and governance especially when Imam Mālik lived through the demise of the Umayyad’s and the rise of the Abbasids.
The way of the scholars of Madinah was to stay independent of governance and to keep it in check when governance went off track. The Muwațța had reached the known world within the life time of the Imam Mālik from Madinah to Spain, central Asia to the Yemen and the regions in between. The intent is to examine the evidence to arrive at a possible date as to when the Muwațța was authored. To examine possible reasons as to why the year 159 AH has been put forward and other dates have not.
The reason why the Muwațța was authored
Ibn ‘Abdul-Barr transmits that; “The first to author a book in Madinah on the meaning of the Muwațța, mentioning what the people of Madinah agreed on [was], ‘Abdul-‘Aziz bin ‘Abdullah bin Abi Salamah al-Mājishūn, a work with no Ḥadith […] it was brought to Mālik he examined it and said, “What an excellent work that has been written, if I were to work on such a work I would begin with Āthār [narrations] then attach words to them.” He said, “Mālik intended on authoring the Muwatta and he authored it, the scholars of Madinah at that time worked on their Muwațțāt.”
Thus the reason for the Muwațța being written was to provide evidence for the school of Madinah, not on any instruction from any monarch or to gather the variant opinions of certain companions of Muḥammad God’s prayer and peace be on him and his family. Al-Mājishūn completed this work before he left for Baghdād with Abbasid king al-Manṣūr died 158 AH when he came to Madinah after the Ḥajj in the year 152 AH. Al-Mājishūn returned to Madinah after 158 AH in the reign of the king al-Mahdī his son ‘Abdul-Malik reports thus. Al-Mājishūn died in Baghdād in 163 AH the king al-Mahdī prayed his funeral prayer and buried him in the Quraysh cemetery of Baghdād.
When was the Muwațța authored?
Thus it can reasonably be accepted that the Muwațța was complete before al-Mājishūn left for Baghdād in the year 152 AH with the Abbasid King al-Manṣūr.
[A side note in 2007 the book of Ḥajj from this book of al-Mājishūn was printed by Dār Ibn Ḥazm edited by Mīklūsh Mūrānī.]
Sa’id bin Abī Hind al-Andalūsī [died 149 AH] took the Muwațța after he had read it to Imam Mālik. The Muwațța had reached al-Andalūs before 150 AH 30 years before Imam Mālik’s death in 179 AH.
The first to take the Masā’il of Mālik to Eygpt was ‘Abdul Rahīm bin Khālīd bin Yazīd al-Jamḥī and ‘Uthmān bin al-Ḥakam. ‘Abdul Rahīm bin Khālīd died 163 AH in Alexandria a narrator of the Muwațța. Imam Ibn al-Qāsīm completed his fiqh studies under ‘Abdul Rahīm in Egypt before he journeyed to Imam Mālik.
A page of Imam ‘Abdul Rahīm bin Khālīd’s riwaya is preserved at Chicago University, hadith from the Muwațța, it is of a Maghrebi student it states I read to ‘Abdul Rahīm for indeed he was saying “related to us ‘Abdul Rahīm bin Khālīd…” … حدثنا عبدالرحيم بن خالد
Thus we can confidently state that the Muwațța had reached Alexandria and Imam ‘Abdul Rahīm bin Khālīd had taught it till he died in 163 AH.
The Muwațța was not taken in a couple of days like now but it took years, then the journey back from Madīnah thus the overwhelming date would have to be before 144 AH. For both these two Imams took from Ibn Jurayj who died in 150 AH and ‘Aqīl bin Khālid al-Aylī who died in 144 AH. Both these Imams only have one journey rihla which ended in 144 AH. Thus they would have had to read the Muwațța to Mālik before 144 AH.
Imam Sha’fī born in 150 AH memorised the Muwațța at the age of 10 by 160 AH, thus the Muwațța had to be completed and well known.
The alternative narrative and a possible reason for that
Shaykh Zahid al-Kawthari et al hold that the Muwațța was written in 159 AH this date goes against the above narrative, a possible reason for this narrative is to rule out any connection of the great Imam Abu Ḥanifah to the Muwațța of the Imam of the abode of the Hijra Mālik bin Anas. The meeting of these great giants is beyond doubt if one benefited from the other does not reduce their greatness Imam Abu Ḥanifah is an Imam as is Imam Mālik. If it is proven that one took from the other it does not reduce their status or rank but shows their zeal for knowledge. Just as the Qaḍī Abu Yūsaf took the Muwațța from Asad bin Furat, Imam Muḥammad Shaybanī took it directly from Imam Mālik as did Imam Shafī’ and that has not reduced their rank but they are great Imams in their own rank. From the above it can be asserted that the Muwațța had been completed by the early 140 AH and there was every possibility for the Imam Abu Ḥanifah to benefit from the work of Imam Malik. This position is strengthened by the following narration by Ibn Abī Ḥātim in his Taqaddimah al-Jarh wal Ta’dīl P3-4.
I heard from Ibraḥim bin Ṭahmān [died 163 AH] saying, “I came to Madinah and I wrote it, then I arrived in Kūfah I went to Abū Ḥanifah in his house I greeted him and he said to me, “From whom have you written from there?” I named [them] to him he said, “Have you written anything from Mālik bin Anas?” I said, “Yes.” He said, “Bring to me, what you have written from him,” I brought to him he called for paper and ink I dictated and he wrote.” Abū Muḥammad said, “Abu Ḥanifah did not write from Ibraḥim bin Ṭahmān from Mālik bin Anas except Mālik bin Anas was alive and indeed approved and [was] trusted by him.”
This narration is rigorously authentic.
What can be understood from this narration is that Imam Abu Ḥanifah benefited by the works of Imam Mālik bin Anas and approved and trusted his work and Imam Mālik bin Anas. This shows the esteem for knowledge that the great Imam had for as it was stated earlier they are all great Imams in their own right.
What blazes through is the soundness of Madinan knowledge and the preservation of it to such a degree that it has become the bedrock of Sunni jurisprudence. For all the founders of Sunni jurisprudence are transmitting directly or indirectly from the Imam of the abode of the Hijrah God be well pleased with each and every one of them and benefit us by their knowledge and understanding.
For sure knowledge is only with God and His Emissary God’s prayer and peace be on him and his family.
 Tartib al-Mudarik Vol 2 P75
 Tartib al-Mudarik Vol 1 P159
 Itiḥāf al-Sālīk P272 and Tabaqāt al-Fuqaha of al-Shirāzī p154