What is the ruling on a Muslim saying to his brother: "May Allah uproot you"?

It is not permissible to supplicate against a Muslim without a reason, unless he is an oppressor, in which case it is permissible to supplicate against him, provided that the supplication does not exceed the extent of the injustice. It is not permissible to supplicate against a disobedient person. The phrase "May Allah uproot you" might be an transgression if its meaning is "May He annihilate you" or "May He remove you," unless the person supplicated against has committed murder or something similar that warrants such a supplication. Allah answered the supplication of Umar ibn Abd al-Aziz to lift oppression from the people, and consequently, Al-Hajjaj and others died. It is best to consult the scholars in your country to understand the meaning of the phrase in your dialect.