Praise be to Allah, and may peace and blessings be upon the Messenger of Allah.
Reincarnation of souls refers to the belief that when a person dies, their soul moves into another body and lives another life, then moves from one body to another according to the deeds they have committed.
This belief is false and contradicts the fundamental belief in resurrection, judgment, and the Hereafter. The Qur'an and Sunnah establish that a person dies and is then resurrected on the Day of Resurrection for judgment and recompense. The soul does not move into other bodies in this worldly life.
Allah تعالى says:
“Every soul will taste death; then to Us you will be returned.” [Al-‘Ankabut: 57]
And He says:
“To Him is your return all together. The promise of Allah is true. He originates creation and then repeats it, so that He may reward those who believe and do righteous deeds with justice.” [Yunus: 4]
Allah تعالى also says:
“Those who disbelieve claim that they will never be resurrected. Say, ‘Yes, by my Lord, you will surely be resurrected; then you will certainly be informed of what you did.’” [At-Taghabun: 7]
It is authentically reported from the Prophet ﷺ that people will be resurrected on the Day of Resurrection barefoot, naked, and uncircumcised, and that their bodies will be restored for the resurrection. He also informed us about the tailbone from which creation will be reconstructed.
Furthermore, what has been established regarding the bliss and punishment of the grave and the questioning by the two angels indicates that after death, a person enters the life of Barzakh, then is resurrected on the Day of Resurrection—not transferred into the body of another human being.
Therefore, the belief in reincarnation contradicts what the messengers brought regarding belief in death, resurrection, judgment, Paradise, and Hellfire.
Whoever holds this belief should be advised with wisdom, and its falsehood should be explained to them using evidence from the Qur'an and Sunnah. They should be called to repent and return to the truth. As for declaring a specific individual to be a disbeliever, this requires that the proof be established against them, that the reality of their belief be known, and that any impediments to such a ruling be absent.
We ask Allah to keep us firm upon monotheism and belief in the Last Day.
And Allah knows best.