Hadrat Imâm-i Rabbânî says in the 17th letter of the third volume of his Maktûbât:
The superiority of the four Khalîfas to one another is in accordance with the sequence of their caliphates. All the savants of the right way said, “After the prophets ‘alaihim-us-salawâtu wa-t-taslîmât’ the highest of human beings is Hadrat Abû Bakr Siddîq ‘radiy-Allâhu anh’. After him is Hadrat ‘Umar Fârûq ‘radiy-Allâhu anh’.”
To this poor person, being higher or superior does not depend on having virtues, attributes or good habits. It depends on accepting Islam before others, giving one’s property more than anybody else for one’s religion, and risking one’s life. That is, it depends on being a teacher to one’s successors. The successors learn eveything from their predecessors.
All of these three conditions were found in Hadrat Siddîq. He accepted Islam before anybody else and sacrificed his possessions and his life for the sake of the religion. This blessing has not been the lot of anybody else besides him in this Ummat. Rasûlullah declared towards his death: “To the extent that Abû Bakr did, there is nobody who sacrificed his property and life for my sake. If I were to have a friend, I would have made Abû Bakr my friend.” He declared in a hadîth: “Allâhu ta’âlâ sent me to you as a prophet. You did not believe. Abû Bakr believed me. He helped me with his property and life. Do not hurt him and revere and respect him!” He declared in a hadîth: “There will not come another prophet after me. If there were another, certainly ‘Umar would be a prophet.” Hadrat Amîr ‘Alî ‘radiy-Allâhu anh’ said, “Both Abû Bakr and ‘Umar are the highest of this ummat. He who holds me superior to them is a slanderer. As slanderers are to be thrashed, I will thrash him.”