The Messenger of Allah ﷺ said, "In Paradise there are one hundred levels, and the distance between each two levels is like the distance between the heavens and the earth. Firdaws is the highest level, from it the four rivers of Paradise gush forth, and above it is the Throne. So when you ask Allah, ask Him for Firdaws."
أن رسول الله ﷺ قال: في الجنة مائة درجة، ما بين كل درجتين كما بين السماء والأرض، والفردوس أعلاها درجة، ومنها تفجر أنهار الجنة الأربعة، ومن فوقها يكون العرش، فإذا سألتم الله، فسلوه الفردوس.
Tirmidhi (2531) narrated it from Abdullah bin Abdul-Rahman, who reported, Yazid bin Harun informed us, Hammam informed us, Zayd bin Aslam narrated to us, from Ata bin Yasar, from Ubada bin Samit, and he related it.The hadith was also narrated by Imam Ahmad (22695) from Yazid bin Harun with the same chain, and in it, "Between every two levels there is a distance of a hundred years' journey."The wording that Tirmidhi presented was narrated by Ahmad from Affan bin Muslim, from Hammam with the same chain. Through this same route it was also narrated by Ibn Khuzayma in Tawhid (184), and by Hakim (1/80), who said, "Its isnad is sahih."