Narrated Ibn Buraidah (RA) on the authority of his father:

The Prophet (ﷺ) appointed a sixth to a grandmother if no mother is left to inherit before her. [Reported by Abu Dawud and an-Nasa'i. Ibn Khuzaimah and Ibn al-Jarud graded it Sahih (authentic) and Ibn 'Adi graded it strong].

وَعَنِ ابْنِ بُرَيْدَةَ , عَنْ أَبِيهِ ; { أَنَّ اَلنَّبِيَّ ‏- صلى الله عليه وسلم ‏-جَعَلَ لِلْجَدَّةِ اَلسُّدُسَ , إِذَا لَمْ يَكُنْ دُونَهَا أُمٌّ } رَوَاهُ أَبُو دَاوُدَ , وَالنَّسَائِيُّ , وَصَحَّحَهُ اِبْنُ خُزَيْمَةَ , وَابْنُ اَلْجَارُودِ , وَقَوَّاهُ اِبْنُ عَدِيٍّ [1]‏ .‏