He is Ubayd Allah b. Mas’ud b. Mahmud b. Ahmad b. Ubayd Allah b. Ibrahim b. Ahmad al-Mahbubi al-Bukhari.
Generally, when Sadr al-Shari’ah is said, it refers to him. He is also called Sadr al-Shariah al-Asghar. The term Asghar (trans. Jr) or Thani (trans. II) is sometimes added after his title to differentiate him from his great grandfather Ahmad b. Ubayd Allah who is also known as Sadr al-Shariah but with the suffix of al-Akbar (trans. Sr) or al-Awwal (trans. I).
His lineage reaches the Ansari Sahabi, Ubadah b. Samit, (may Allah be pleased with him) via Mahbub b. Walid b. Ubadah b. Samit and hence the family name of Mahbubi. He was born into a family with a long line of reputable and accomplished scholars. His father was Jamal al-Din Mas’ud. His grandfather was the great scholar Taj al-Shariah Mahmud, the author of the authoritative book on the Hanafi fiqh entitled Wiqāyah. His great grandfather was Sadr al-Shariah al-Akbar, the author of Talqih al-‘Uqul.
Due to the names and titles in his lineage being somewhat similar and repetitive such as the multiple occurrences of Ubayd Allah, Mahmud, Ahmad and Sadr al-Shariah, many biographers, including Haji Khalifa, have made errors in stating the proper lineage which in turn leads to difficulty in identification. Allm. Abdul Hayy Lacknawi discusses the issue in detail in Fawā’id al-Bahiyyah.
His date of birth is not recorded in the well known bio-dictionaries. He died on 747 AH (1346 CE) and was buried in Bukhara.
The fuqaha consider him reliable. He is mentioned with esteem and respect by authoritative scholars when referenced in their work. The style of his writing hint that he was a person who had attention to detail and was cautious in nature. He seems to avoid waste and opts to convey messages succinctly. His genre of writing suggest a deep loyalty to the tradition, affinity to preserve the Din and protect it from convolution.
Sadr al-Shari’ah al-Asghar studied under his father Jamal al-Din Mas’ud as well as his grand father Taj al-Shariah Mahmud, the author of Wiqāyah which is reported to have been written so that Sadr al-Shariah himself could memorise the core edicts in Hidāyah. Both these works are now considered the standard text in the Hanafi fiqh. His educational pedigree in the Hanafi fiqh goes sequentially from Taj al-Shariah Mahbubi to his father Sadr al-Shariah al-Akbar Mahbubi to his father Jamal al-Din Ubayd Allah Mahbubi to Mufti Imam Zadah to Imad al-Din to his father Shams al-A’immah Zaranjari to Shams al-A’immah Sarakhsi to Shams al-A’immah Hulwani to Abu Ali Nasafi to Muhammad b. Fadl to Sabzmuni to Abu Abd Allah b. Abi Ja’dh al-Kabir to his father to Imam Muhammad b. Hasan al-Shaybani.
His expertise expanded to many fields including Hadith, Fiqh, Usul, Aqa’id, logic, grammar, rhetoric poetry. He researched assiduously and wrote meticulously. His knowledge was vast and incisive through which he was able to summarise many important and difficult topics succinctly. Allāmah Abd al-Hayy Lacknawi writes that all the works of Sadr al-Shariah are accepted by the reliable scholars amongst the fuqaha. As such he is frequently referenced in later authoritative works.
His works include Ta’dīl al-Ulūm, Washshah, Nuqāyah, Tanqīh and its commentary Tawdīh. The last three are of particular note. Nuqāyah (a summary of Wiqāyah) is a classic and is deemed one of the matn (authoritative texts) in the Hanafi Fiqh. Mulla Ali Qari has written an excellent commentary upon it entitled, Fath Bāb al-‘Ināyah. Similarly, Tanqīh with Tawdīh which summarises the Hanafi and the Mutakallim approaches in Usul Fiqh is also a classic and authoritative text in that genre. Allāmah Taftazani has written a notable commentary upon it entitled, Talwīh.
 Some have erroneous declared the name here to be Umar instead of Mahmud.
 Some have erroneously declared the name here to be Mahmud instead of Ibrahim.
 I have seen some state the date of death to be 630 AH but no source have been stated.
 Sayyid Mutadha al-Husayni in Fawā’id al-Bahiyyah (p. 110). The entire lineage is stated as Ubayd Allah b. Mas’ud b. Taj al-Shari’ah Mahmud b. Sadr al-Shariah Akbar Ahmad b. Jamal al-Din Abi Makarim Ubayd Allah b. Ibrahim b. Ahmad b. Abd al-Malik b. Umayr b. Abd al-Aziz b. Muhammad b. Ja’far b. Khalf b. Harun b. Muhammad b. Muhammad b. Mahbub b. Walid b. Ubadah b. Samit.
 Lacknawi, Abd al-Hayy. Fawā’id al-Bahiyyah p. 112
 Allm. Qasim b. Qutlubgha. Taj al-Tarajim
 Fawā’id al-Bahiyyah p. 112
Bibliography: al-Jawāhir al-Mudhiyyah, al-Tabqāt al-Sunniyah, Tāj al-Tarājim, Kashf al-Zunūn, Fawā’id al-Bahiyyah, al-A’lam li al-Ziraqli
Courtesy of DIBAJ Islamic Studies Bulletin, Number 4 (2013)