Targum zu Dewarim 27:26

The twelve tribes, each and every, shall pronounce the blessings altogether, and the curses altogether. In blessing, they shall turn their faces (in pronouncing) word by word towards Mount Gerezim, and shall say: Blessed is the man who confirmeth the words of this law to perform them. In cursing, they shall turn their faces towards Mount Ebal, and say: Accursed is the man who confirmeth not the words of this law to perform them. And all shall answer together, and say, Amen. These words were spoken at Sinai, and repeated in the tabernacle of ordinance, and (again) the third time on the plains of Moab, in twelve sentences (words), as the word of every tribe; and each several commandment (was thus) ratified by thirty and six adjurations.