Buddha Mahavairochana spontaneously composes the 21 Praises to Goddess Tara.
Princess Metok Zay, (Beautiful Flower) made vast offerings and dedications, performing generous, courageous, patient, and compassionate activities of the greatest virtue on behalf of sentient beings. Buddha Mahavairochana asked Princess Beautiful Flower what it was she wished for, what was the intent of her heart, she replied, "I shall remain in this world until every single being is fully liberated." This was a joyful surprise to the Buddha, who had never heard anyone offer such a noble, selfless, and courageous aspiration. In response to her personal sacrifices, her virtue and aspirations, and inspired by her wishes on behalf of beings, Buddha Vairochana spoke spontaneously the prayer of the twenty-one praises to Tara, a praise to twenty-one qualities of Tara.

"Virtually every Tibetan monastery performs Green Tara puja prayer rituals every morning, whether they have five monks or one thousand. The praise to the twenty-one Taras has been chanted continuously by countless beings stretching all the way back to Buddha Vairochana in an earlier age long, long before our present era. The fact that this prayer is so ancient and has been so popular and widely practiced over the ages contributes to its great power and effectiveness.
All the accumulated blessings of that have arisen due to the prayers of the faithful throughout the ages come down to us and are received by us when we pray with faith and devotion to Tara. Through regular practice of the praise to the twenty-one Taras and the mantras of Tara, these blessings are cultivated and can ripen in our mindstreams, in our experience. It is for this reason that the worship of Tara makes such an excellent daily practice. "
His Eminence Chogye Trichen Rinpoche. Read the Full Story The Practice of the Goddess Green Tara