And when the Blessed One had set the Wheel of Dhamma in motion, the earth devas cried out: "At Varanasi, in the Game Refuge at Isipatana, the Blessed One has set in motion the unexcelled Wheel of Dhamma that cannot be stopped by priest or contemplative, deva, Mara or God or anyone in the cosmos." On hearing the earth devas' cry, the devas of the Four Kings' Heaven took up the cry... the devas of the Thirty-three... the Yama devas... the Tusita devas... the Nimmanarati devas... the Paranimmita-vasavatti devas... the devas of Brahma's retinue took up the cry: "At Varanasi, in the Game Refuge at Isipatana, the Blessed One has set in motion the unexcelled Wheel of Dhamma that cannot be stopped by priest or contemplative, deva, Mara, or God or anyone at all in the cosmos."
And in that time of the people with an eighty-thousand-year life-span, there will arise in the world a Blessed Lord, an arahant fully enlightened Buddha named Metteyya, endowed with wisdom and conduct, a Well-farer, Knower of the worlds, incomparable Trainer of men to be tamed, Teacher of gods and humans, enlightened and blessed, just as I am now.
So, how is it that a Buddha can arise when the unstoppable wheel of Dhamma has been set in motion? Furthermore, should we assume that previous Buddhas have not set in motion an "unstoppable" Dhamma?