All praise is due to Allah, and peace and blessings be upon the Messenger of Allah.
The Qur'an and the authentic Sunnah do not establish the location of the grave of Adam (peace be upon him). There is no authentic evidence identifying where he was buried, so it is not permissible to assert that his grave is in any particular country or place.
The scholars have stated that, among the graves of the prophets, the only one whose location is known with certainty is the grave of Prophet Muhammad ﷺ in Madinah. As for the grave of Prophet Abraham (peace be upon him) in the city of Hebron (Al-Khalil) in Palestine, the majority of scholars held that it is indeed his burial place, although some scholars refrained from affirming this with certainty.
Some narrations claim that Adam (peace be upon him) was buried in Makkah, Jerusalem, or elsewhere. However, these reports are not authentic because their chains of transmission are weak or they originate from the Isra'iliyyat (reports from Jewish and Christian traditions). Therefore, they cannot be relied upon in matters of the unseen.
For this reason, a number of scholars stated that the location of Adam's grave is unknown, and whoever claims to know its location speaks about Allah without knowledge.
It is popularly claimed by some people that Adam (peace be upon him) descended in Sri Lanka, or that his footprint or grave is located there. However, there is no basis for these claims in the Qur'an or the authentic Sunnah, nor have they been established by any reliable scholar through authentic evidence.
Scholars have explained that one of the wisdoms behind the unknown locations of most prophets' graves is to block the means to exaggeration in honoring them, or turning their graves into places of worship or seeking blessings. Had knowing the locations of these graves been part of the religion, Allah would have preserved them just as He preserved His Book and the Sunnah of His Prophet ﷺ.
It is not correct to specify the location of Adam's grave, as no authentic evidence from the Qur'an or the Sunnah establishes it. The claims that his grave is in Makkah, Jerusalem, Sri Lanka, or elsewhere are unsupported by reliable evidence. Therefore, Muslims should refrain from making claims about matters that have not been authentically established and should avoid spreading weak reports on this subject.
And Allah knows best.