“It is impossible, mendicants, it cannot happen for two perfected ones, fully awakened Buddhas to arise in the same solar system at the same time. But it is possible for just one perfected one, a fully awakened Buddha, to arise in one solar system.”
Read this translation of Aṅguttara Nikāya 1.277 by Bhikkhu Sujato on SuttaCentral.net. Or read another translation on SuttaFriends.org. Or read the Pāli on DigitalPaliReader.online.
Or read a translation in other languages.