In Majjhima Nikaya, it's in 3.123 not 124. I'll quote the sutta Acchariya-abbhuta for you:
I heard and learned this from the Blessed One's own lips: 'When the Bodhisatta passed away from the Tusita heaven and descended into his mother's womb, then a great immeasurable light surpassing the splendour of the gods appeared in the world with its gods, its Maras, and its Brahmas, in the generation with its recluses and brahmins, with its princes and its people. And even in those abysmal world interspaces of vacancy, gloom, and utter darness, where the moon and the sun, mighty and powerful as they are, cannot make their light prevail--- there too a great immeasurable light surpassing the splendour of the gods appeared. And beings reborn there perceived each other by that light: "So indeed sir, there are other beings reborn here!" And this ten-thousandfold world system shook and quaked and trembled, and there too a great immeasurable light surpassing the splendour of the gods appeared.' This too I remember as the wonderful and marvelous quality of the Blessed One.
The term "ten-thousandfold world system" is referring to a galaxy according to Buddhist cosmology.