"And We made them leaders, guiding (men) by Our Command, and We sent them inspiration to do good deeds, to establish regular prayers, and to practise regular charity; and they constantly served Us (and Us only)."
 

(Holy Qur'an (Yusufali) 21:73)

"But this earth will never be without such persons who will prove universality of truth as disclosed by the Lord, they may be well known persons, openly and fearlessly declaring the things revealed to them; or they may, under fear of harm, injury or death, hide themselves from the public gaze and may carry on their missions privately so that the reasons proving the reality of truth as preached by religion and as demonstrated by His apostles may not totally disappear. How many are they and where could they be found? I swear to God that they are few in number, but their worth and their ranks before God are very high. Through them the Lord preserves His Teachings so that they, while departing, may hand over these truths to persons like themselves. The knowledge which they have acquired has made them see the realities and visualize the truth, and instilled in them the spirit of faith and trust. The duties which were decreed as hard and unsufferable by ease loving and easy going people are considered easy and bearable by them. They feel happy in the company and association of things which frighten the ignorant and uneducated. They live in this world like everybody else but their souls soar the heights of Heavenly eminence. They are delegates of God on this earth and they invite people towards Him. How I love to meet them!"
 

(Nahjul Balagha: Sermons, letters and saying of Hazrat Ali (Second American edition, 1981), Sayings of Hazrat Ali 146, p. 290)