Sheikh al-Mufeed (a.r) in his book ‘Al-Amali’ after narrating the chain of narration said that Abdullah Ibn Abbas said:
When Allah’s Messenger, Prophet Muhammad (peace be upon him and his pure progeny) was on his deathbed, he cried until tears overtook his beard.
So he was asked: ‘What makes you cry, Messenger of Allah?’
The Prophet (saww) answered: ‘I am crying for my progeny, for the crimes that will be committed against them by the evildoers of my nation after my death. It is as if I (can see) my daughter, Fatima, being oppressed and crying: “O Father!” But no one will come to help her among my Ummah.’
Fatima (A.S.) began weeping when she heard this, so the Prophet said to her: ‘Do not cry my daughter’
She said: ‘I am not crying because of that which will be done to me after you; rather, I am crying because I will be separated from you, Messenger of Allah’
He then said: ‘Rejoice, O daughter of Muhammad (saww), at the close succession to me, for you will be the first one to follow me from among my Ahlul-Bayt (peace be upon them all).’
(Source – Behar ul Anwar, vol 43)