The Prophet ﷺ said, "The first man to enter through this door is one of the people of Paradise." Then Saad bin Abu Waqqas entered.
حدثنا قتيبة بن سعيد أخبرنا رشدين عن الحجاج بن شداد عن أبي صالح الغفاري
أن النبي ﷺ قال أول من يدخل من هذا الباب رجل من أهل الجنة فدخل سعد بن أبي وقاص
Its chain is daif, because of the weakness of Rushdin bin Saad, as we explained in detail in the commentary on 5748. Hajjaj bin Shaddad Sanaani, from Sanaa of Syria, is trustworthy, Ibn Hibban confirmed him as trustworthy, and Bukhari mentioned him in al-Kabir 1/2/374.Abu Salih Ghifari, whose name is Saeed bin Abdul-Rahman, is a trustworthy successor. Ibn Hibban mentioned him in al-Thiqat, and Bukhari mentioned him in al-Kabir 2/1/449.The glad tidings of Paradise given to Saad bin Abu Waqqas are established through cumulative corroborating reports found in many hadiths, including one that has already appeared in the Musnad of Abdul-Rahman bin Awf, 1675.As for this particular hadith, I have not found it anywhere else after lengthy search and pursuit, and Haythami did not mention it in Majma al-Zawaid in the place where it would be expected. Perhaps it is there in some spot I have not managed to reach.