Halakha Mazmur 145:2: Mishneh Torah, Blessings

For a practice that is only customary, even if traced to the prophets, for example, taking the willow branch on the seventh day of the feast of Tabernacles, and—needless to add—if it is ascribed to the Sages, for example, reciting the Hallel^*Psalms 113-118 omitting 115:1-11 and 116:1-11. on new moons and the intermediate days of Passover, no blessing is to be recited at its performance.^*In the Ashkenazi ritual, a blessing is recited. Thus also any act, in regard to which you are in doubt whether it requires a blessing or not, should be performed without a blessing. One should always carefully avoid saying blessings unnecessarily; and should be heedful to recite, as often as there may be occasion, the blessings that are requisite. And so David said "Every day I will bless Thee and praise Thy name forever" (Ps. 145:2).