Hazrat Umme Salma (R.A) narrates that I swear upon Allah on whom I take oaths that Hazrat Ali (R.A) was most near to the Apostle of Allah (PBUH) in terms of commitment and position. She narrates that we used to enquire the health of Prophet (PBUH) every other day and the Prophet (PBUH) admitte that Ali (R.A) came most for enquiring my health. She narrates that she thought the Allah's Apostle (PBUH) has sent Hazrat Ali (R.A) for some urgent work and after that when Hazrat Ali (R.A) visited the Prophet (PBUH), then I supposed that he has some work with the Prophet (PBUH), so we came out and stayed near the door and I was sitting most near to the door. Hazrat Ali (R.A) was bowed on Prophet (PBUH) and whispered something and after that day the Allah's Apostle died. It shows that Hazrat Ali (R.A) was most near to Prophet Muhammad (PBUH) in terms of obligation and commitment. (Imam Ahmed, Imam Hakim)
Hazrat Ali (R.A) refers that Prophet (PBUH) said: May Allah show mercy on Abu Bakar (R.A) that he gave his daughter in my Nikkah and brought me to Dar ul Hijra and also set free Bilal (R.A) by paying for his freedom from his personal earnings. May Allah show mercy to Hazrat Umer (R.A) that he always speaks truth whether it is bitter for others and for this reason he has no friend. May Allah show mercy on Usman (R.A) that even angels show shyness to him due to his modest nature and may Allah show mercy on Ali (R.A). O Allah; be the truth with him wherever he is. (Imam Tarimzi, Imam Hakin, Imam Tibrani)
Hazrat Abu Rafay (R.A) refers that Prophet (PBUH) sent Hazrat Ali (R.A) to some place, when he returned back than Prophet (PBUH) said that Allah, His Prophet (PBUH) and Gabriel are pleased with you, (Tibrani)
