The Messenger of Allah ﷺ said, "An opening like this has been made in the barrier of Yajuj and Majuj," and he formed a ring with his fingers, joining them together.
حدثنا يحيى بن إسحاق أخبرني وهيب أخبرني ابن طاوس عن أبيه
قال رسول الله ﷺ فتح من ردم يأجوج ومأجوج مثل ذلك وحلق تسعين وضمها
Its isnad is sahih. Bukhari related it, 4/168, in "The Prophets," under the saying of Allah, "And they ask you about Dhul-Qarnayn", and Muslim in "Tribulations and the Signs of the Hour," 4/2208, no. 2881, and Tirmidhi, 4/480, no. 2187, in the book of "Tribulations," concerning the emergence of Yajuj, and Ibn Hibban, 470, no. 1906. Ibn Tawus is Abdullah bin Tawus bin Kaysan. Both he and his father were trustworthy, well-known jurists.