Bismillah.
Hadith no. 1118 is a repeat. It's about Najashi's death and funeral prayer. Read on it here.
Narrated Abu Huraira:
A black person, a male or a female used to clean the Mosque and then died. The Prophet (p.b.u.h) did not know about it . One day the Prophet remembered him and said, "What happened to that person?" The people replied, "O Allah's Apostle! He died." He said, "Why did you not inform me?" They said, "His story was so and so (i.e. regarded him as insignificant)." He said, "Show me his grave." He then went to his grave and offered the funeral prayer.
Read about delayed funeral prayer here.
One of the questions we'll be asked in our graves is about the Messenger (SAW). And we'll only be able to say what we 'really' believed and acted upon. Read further to see how a believer will answer and how a non-believer/hypocrite will answer the same question.
Narrated Anas:
The Prophet said, "When a human being is laid in his grave and his companions return and he even hears their foot steps, two angels come to him and make him sit and ask him: What did you use to say about this man, Muhammad? He will say: I testify that he is Allah's slave and His Apostle. Then it will be said to him, 'Look at your place in the Hell-Fire. Allah has given you a place in Paradise instead of it.' " The Prophet added, "The dead person will see both his places. But a non-believer or a hypocrite will say to the angels, 'I do not know, but I used to say what the people used to say!' It will be said to him, 'Neither did you know nor did you take the guidance (by reciting the Quran).' Then he will be hit with an iron hammer between his two ears, and he will cry and that cry will be heard by whatever approaches him except human beings and jinns."
Another version of this narration has been posted previously. Here's the link.
May Allah make us true followers of Muhammad (SAW)), and may we be able to answer the questions in grave correctly and see our places in Paradise right there. May we rise as the ummati(s) of Muhammad (SAW) on the Day of Judgement, and may we be served from Al-Kauthar that day. May we get his company in Jannat-ul-Firdaws. May we really love him.
Wassalam.