One should be careful not to sing songs that contain pesukim (verses) of Tehillim, or pesukim in general, in proximity to idol worshippers.
Sources and Explanations
This is brought in Sefer Chassidim (siman 238): “A person should not teach a galach (priest) letters, nor should he play a pleasant melody before him, lest the priest play that same melody in his idolatry; and any melody that is played before idolatry, one should not make that melody for Hakadosh Baruch Hu.” He also brought this a second time (siman 429): “If there is a heretic who wishes to compose a piyyut for idolatry, or a gentile who wishes to make [a song] for sin, and he says to a Jew, ‘Tell me a pleasant melody with which you praise your God,’ he should not tell him, so that it should not come about through him.”
From the sefer “Shaf Veyativ – Laws of Saying Tehillim” by Rabbi Shay Tahan, Chapter 7: What Is Forbidden and Permitted When Saying Tehillim, Halacha 21 (p. 132 in the print edition). Translated from the Hebrew original.
