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 as mentioned.Imam Ahmad (22695) also narrated this hadith from Yazid bin Harun through the same chain, and in it there occurs, "Between every two levels is a distance of a hundred years' journey."The wording that Tirmidhi presented was also narrated by Ahmad from Affan bin Muslim, from Hammam, through the same chain. Through this same route, Ibn Khuzayma also narrated it in Tawhid (184), as did Hakim (1/80), who said, "Its isnad is sahih."