Please guide me.
Is it a hadith that ' it is better to name a grandson on the name of his grand father'

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.

As far as we know, there is no Hadeeth that recommends naming a child after his grandfather, but if it is part of the customs in some societies to name a child after his grandfather, then it is recommended to do so, since this is considered a form of dutifulness to the grandfather and a means of bringing joy to his heart. Nonetheless, this should not be done if the name of the grandfather implies prohibited meanings such as slavery to other than Allaah The Almighty as clarified in Fataawa 87262 and 82724.

However, we have taken customs into consideration here because in some societies grandfathers dislike that their grandchildren are named after them during their life.

Allaah Knows best.