Sayyiduna Mu'awiyah bin Haydah (may Allah be pleased with him) narrates this saying of the Prophet (peace and blessings be upon him): "You complete the number of seventy nations; you are the last of them and the most honoured of them before Allah Almighty. Between the two leaves of a door of Paradise is a distance of forty years' travel, and a day will come upon it when it will be crowded." (Allamah al-Haythami says:) I say: Al-Tirmidhi and others recorded part of this narration.
Ahmad recorded it; its narrators are thiqat (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب أهل الجنة / 18645