This is a ḥadīth that we do not know as marfūʿ except through this chain.

Some of the Companions of the Prophet, may Allah bless him and grant him peace, gave the grandmother a share of inheritance along with her son, while others did not give her a share.

12 – Chapter: What has been reported concerning the inheritance of the maternal uncle

2235 – Bundār narrated to us, saying: Abū Aḥmad al-Zubayrī narrated to us, saying: Sufyān narrated to us, from ʿAbd al-Raḥmān ibn al-Ḥārith, from Ḥakīm ibn Ḥakīm ibn ʿAbbād ibn Ḥunayf, from Abū Umāma ibn Sahl ibn Ḥunayf, who said: ʿUmar ibn al-Khaṭṭāb sent with me a letter to Abū ʿUbayda stating that the Messenger of Allah, may Allah bless him and grant him peace, said: "Allah and His Messenger are the mawlā of the one who has no mawlā, and the maternal uncle is the heir of the one who has no heir."(1)

On this topic there is also a report from ʿĀʾisha and from al-Miqdām ibn Maʿdī Karib.

This is a ḥasan ḥadīth.(2)

2236 – Isḥāq ibn Manṣūr informed us, saying: Abū ʿĀṣim informed us, from Ibn Jurayj, from ʿAmr ibn Muslim, from Ṭāwūs--------------------------------------------
= Ibn Manṣūr (95), Ibn Abī Shayba 11/331 and 333, and from al-Ḥasan al-Baṣrī according to Saʿīd ibn Manṣūr (96), and Ibn Ḥazm 9/281, and the chains to them are sound.

(1) Ṣaḥīḥ bi-ghayrihi; it was also recorded by Ibn Mājah (2737), al-Nasāʾī in al-Kubrā (6351), and it is in al-Musnad (189) and Ṣaḥīḥ Ibn Ḥibbān (6037). It is supported by the ḥadīth of ʿĀʾisha and the ḥadīth of al-Miqdām ibn Maʿdī Karib.

(2) Added in the printed edition: ṣaḥīḥ, but it is not found in our manuscript sources, nor in Tuḥfat al-Ashrāf, nor in the copy of al-Mubārakfūrī.