Many sources mention the shajra nasb of Prophet Muhammad ﷺ.
a) Do we have the shajra established from authentic riwayat?
b) Does any reference to shajra mention the timeline/age of the ancestors in the family till Adam AS.
c) Is it possible to determine the approximate date of Adam alayhi salam era on earth on modern or hijri calendars?
Bismillahi Ta’ala
Walaikum Assalam Warahmatullah
a & b) The lineage of Rasulullah ﷺ is mentioned in Sahih Bukhari until Ma’ad ibn Adnaan (معد بن عدنان). Imam Baghawi RA has written that this much of the genealogy is authentic and is consensual. Scholars have extended the lineage until Sayyidina Adam AS, however the extension after Adnaan is controversial and not authentic.
c) Scholars have attempted to produce a rough estimate of how long ago Sayyidina Adam AS was created. The estimates given by Muslim historians range from 4,000 years to hundreds of thousands of years. Only Allah knows the exact number.
Wallahu A’lam
And Allah Ta’āla Knows Best
Mufti Faisal al-Mahmudi