Q. I sang at end of Aleinu, v’ne’emar v’haya Hashem…. and one guy yelled at me that I can’t repeat a phrase where Hashem’s name is. Where is the source for that? I have been singing this my whole life. It is definitely not in the Torah.
Thank you

A. Shulchan Aruch (O.H. 215: 4) rules that whoever recites an unnecessary bracha, transgresses the prohibition of uttering the Name of Heaven uselessly. (Third Commandment) Mishna Berurah (ibid. 19) adds that this (rabbinically) applies even when it is recited in a manner of praise and veneration, since it is not needed.

Remoh (O.H. 188: 7), suggests that if one forgot to say Yaaleh Veyavoh in Birchas Hamazon during Rosh Chodesh, he may append it to the Horachamons recited at the end. He then adds that since it not essential and Yaaleh Veyavoh does contain repeated mentions of the Name of Hashem, it is better to omit it. He points out that this is the generalized tradition. Magen Avraham (ibid. 11) wonders why, and writes;” do we not all day repeat constantly prayers that contain the name of Hashem, why should this be different?”. Biur Halacha (ibid.) differentiates between an established obligated bracha and a tefilah or praise said to Hashem from one’s heart.

In practice, many repetitiously sing variations of the seven names of Hashem while chanting the Zemiros of Shabbos (as in Boruch Kel Elyion etc.), However, Poiskim write that when possible it should be avoided. (Piskey Teshuvos 215: 18, see also Betzel Hachochmo 4: 52, where he permits repeating Selichos for the Tzibur, when no one else can recite them in a second minyan).

Horav Shlomo Miller’s Shlit”a opinion is that Tefilos should be recited as fervent and moving requests to Hashem, and not as songs to entertain the attending. Repetitions, when they do not meet the above criteria, should be avoided. (Regardless of the questionable permissibility of the unnecessary repetition of the name of Hashem, embarrassing publicly the prayer leader is certainly severely prohibited).

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a