So it is between the two of you, and whichever of you is alone with him, it is for her. (1)

This is a ḥasan ṣaḥīḥ ḥadīth, and it is more authentic than the ḥadīth of Ibn ʿUyaynah. On this topic, there is also a narration from Buraydah.

11 – Chapter: What has been reported regarding the inheritance of the grandmother along with her son

2234 – Al-Ḥasan ibn ʿArafah narrated to us, he said: Yazīd ibn Hārūn narrated to us, from Muḥammad ibn Sālim, from al-Shaʿbī, from Masrūq,
from ʿAbd Allāh, who said regarding the grandmother along with her son: She was the first grandmother to whom the Messenger of Allāh, peace and blessings be upon him, gave a sixth along with her son, while her son was still alive. (2)

--------------------------------------------
(1) Ṣaḥīḥ bi-ghayrihi, like the one preceding it.
(2) Ḥasan bi-ghayrihi as a marfūʿ narration, and it has been authentically established as mawqūf, as will be explained. The defect here is Muḥammad ibn Sālim — al-Hamdānī al-Kūfī — for he is abandoned in ḥadīth, and he alone narrated it as marfūʿ and mentioned the intermediary between al-Shaʿbī and Ibn Masʿūd.
It was also narrated as marfūʿ by Ibn Ḥazm in al-Muḥallā 9/281, and al-Bayhaqī 6/226, via the chain of Yazīd ibn Hārūn, from Muḥammad ibn Sālim, with this isnād.
It was also narrated by al-Dārimī (2932) via the chain of Muḥammad ibn Sīrīn, and Saʿīd ibn Manṣūr (99) and (110), and Ibn Ḥazm 9/279 via the chain of ʿĀmir al-Shaʿbī — both from Ibn Masʿūd that he said: The first grandmother who was given the sixth was the paternal grandmother along with her son — this is the wording of Saʿīd ibn Manṣūr in the first place, and the rest are similar to it. Ibn Sīrīn and al-Shaʿbī did not hear from Ibn Masʿūd.
It was also narrated as mawqūf on Ibn Masʿūd by ʿAbd al-Razzāq (19090), Saʿīd ibn Manṣūr (109), Ibn Abī Shaybah 11/331, Ibn Ḥazm 9/279, and al-Bayhaqī 6/226, and its isnād with them is ṣaḥīḥ except for the isnād of ʿAbd al-Razzāq, for it contains a discontinuity.
The ḥadīth was also narrated as mursal from Ibn Sīrīn by ʿAbd al-Razzāq (19093), and Saʿīd =