Narrated Abu Said Al-Khudri: The Prophet said, “When the people of Paradise will enter Paradise and the people of Hell will go to Hell, Allah will order those who have had faith equal to the weight of a grain of mustard seed to be taken out from Hell. So they will be taken out but (bythen) they will be blackened (charred). Then they will be put in the river of Haya’ (rain) or Hayat (life) (the Narrator is in doubt as to which is the right term), and they will revive like a grain that grows near the bank of a flood channel. Don’t you see that it comes out yellow and twisted”
Sahih Buhkari Volume 1, Book 2, Number 21:

Raising doubts in The Holy Prophet’s (Sallalaahu Alahi wassallam) command is a grievous sin, disrespecting him is destroying faith, Allah’s will is in his will.

Narrated ‘Aisha: Whenever Allah’s Apostle ordered the Muslims to do something, he used to order them deeds which were easy for them to do, (according to their strength and endurance). They said, “O Allah’s Apostle! We are not like you. Allah has forgiven your past and future sins.” So Allah’s Apostle became angry and it was apparent on his face. He said, “I am the most God-fearing, and know Allah better than all of you do.”
Sahih Bukhari Volume 1, Book 2, Number 19:

Here the people wanted to do more than that what the Holy Prophet ordered, and claimed that the sins of the Holy Prophet Muhammed Sallalaahu Alaihi wasallam are already forgiven but thiers are not, so they taught they need to do more, They were a few things which made the Prophet angry and though they did not become Khawarij like those who disrespected him directly, Still anger was displayed on his blessed face

1) The people did not recognize that Obeying the Holy Prophet Sallalaahu alaihi wasallam is Obeying Allah

2) They tried to compete with him like he is an ordinary human being like them and did not recognize his exceptional status bestowed upon him

3) The Holy Prophet Muhammed Sallalaahu Alaihi wasallam is the biggest intercessor for the forgiveness of sins

These reasons are apparent but they could be many more

Destruction of Deeds and Imaan with disrespect to the Holy Prophet and anything associated with the Holy Prophet Muhammed Sallalaahu Alaihi wasallam.

Those who disrespected the Holy Prophet Muhammed Sallalaahu Alahi wasallam directly or anything associated with him directly like his city which he loved Madina, or his beloved Sahaba or Ahle Bayt have indulged in a sin which destroyed all deeds and their faith

Narrated Sad: I heard the Prophet saying, “None plots against the people of Medina but that he will be dissolved (destroyed) like the salt is dissolved in water.”
Sahih Bukhari Volume 3, Book 30, Number 101:

Narrated Abu Sa’id: While the Holy Prophet (Sallallahu Alaihi Wasallam) was distributing (something), ‘Abdullah bin Dhil Khawaisira At-Tamimi came and said, “Be just, O Allah’s Apostle!” The Prophet (Sallallahu Alaihi Wasallam) said, “Woe to you! Who would be just if I were not?” ‘Umar bin Al-Khattab(radiallahu taala anhu ) said, “Allow me to cut off his neck! ” The Prophet (Sallallahu Alaihi Wasallam) said, ” Leave him, for he has companions, and if you compare your prayers with their prayers and your fasting with theirs, you will look down upon your prayers and fasting, in comparison to theirs. Yet they will go out of the religion as an arrow darts through the game’s body in which case, if the Qudhadh of the arrow is examined, nothing will be found on it, and when its Nasl is examined, nothing will be found on it; and then its Nadiyi is examined, nothing will be found on it. The arrow has been too fast to be smeared by dung and blood. The sign by which these people will be recognized will be a man whose one hand (or breast) will be like the breast of a woman (or like a moving piece of flesh). These people will appear when there will be differences among the people (Muslims).” Abu Sa’id(radiallahu taala anhu ) added: I testify that I heard this from the Prophet(Sallallahu Alaihi Wasallam) and also testify that ‘Ali (May Allah be pleased with him ) killed those people while I was with him. The man with the description given by the Prophet(Sallallahu Alaihi Wasallam) was brought to ‘Ali(may Allah be pleased with him). The following Verses were revealed in connection with that very person (i.e., ‘Abdullah bin Dhil-Khawaisira At-Tarnimi):

‘And among them are men who accuse you (O Muhammad(Salallahu Alaihi wasallam)) in the matter of (the distribution of) the alms.’ (9.58)
Sahih Al Bukhari Volume 9, Book 84, Number 67

You will get up with the ones you love
Narrated by Anas

A man asked the Prophet about the Hour (i.e. Day of Judgment) saying, “When will the Hour be?” The Prophet said, “What have you prepared for it?” The man said, “Nothing, except that I love Allah and His Apostle.” The Prophet said, “You will be with those whom you love.” We had never been so glad as we were on hearing that saying of the Prophet (i.e., “You will be with those whom you love.”) Therefore, I love the Prophet, Abu Bakr and ‘Umar, and I hope that I will be with them because of my love for them though my deeds are not similar to theirs.
(Sahih- al-Buhkhari Volume 5 Hadith 37)

Loving someone for Allah’s sake
“It is narrated by Mu‘adh bin Jabal that he heard the Messenger of Allah saying:

Allah the Exalted and Almighty said: ‘My love has been made obligatory for those two persons who love each other on My count and spend time together for My sake, and see each other for My sake and give money to each other generously for My sake.’”

This sahih (sound) hadith narrated by Malik bin Anas in al-Muwatta, b. of sha‘ar (hair) ch.5 (2:954#16), and Ibn ‘Abd-ul-Barr said its chain is good. Ahmad bin Hambal also transmitted it in his Musnad (5:233); Hakim in al-Mustadrak (4:169), who graded it sahih, and also confirmed by Dhahabi; Baghawi in Sharh-us-sunnah, (13:49-50#3463); Khatib Tabrizi in Mishkat-ul-masabih, b. of adab (good manners) ch.16 (3:75#5011).