A man came to Abu Darda' while he was in Damascus. Abu Darda' asked him "What has brought you here, my brother?" He replied, "A hadith which you relate from the Prophet (saw). Abu Darda' asked, "Have you come for some worldly need?" He replied, "No." "Have you come for business?" He said, "No." "You have come only to seek this hadith?" He said, "Yes."
Abu Darda' then said, "I heard the Messenger of Allah (saw) say: 'Whoever travels a path seeking sacred knowledge, Allah will place him on a path leading to Paradise. The angels lower their wings for the student of sacred knowledge, pleased with what he is doing. The creatures in the heavens and earth seek forgiveness for the student of sacred knowledge, even the fish in the water. The superiority of the religious scholar over the devout worshipper is like the superiority of the full moon over the other heavenly bodies. The religious scholars are the heirs of the prophets. The prophets leave no money as a bequest, rather they leave knowledge. Whoever seizes it has taken a bountiful share." (Imam Ahmad, Abu Dawood, at-Tirmidhi, ibn Majah)
The early generations of Muslims, owing to the strength of their desire for sacred knowledge, would journey to distant lands seeking a single prophetic hadith - without hesitation in order to seek out knowledge that they lacked themselves.
A striking example of this sort of journey is what Allah relates in the Qur'an about Prophet Moses' (as) journey with his young companion. If there ever existed a person who had no need to travel to seek knowledge, it was Moses (as), for Allah had spoken to him and given him the Torah in which all divine principles had been revealed then. Still, when Allah informed him of a man (named Khidr) who had been favoured with knowledge, Moses inquired about meeting him, and then set out with his young companion to find this Khidr, as Allah the Exalted says:
"And behold! Moses said to his young companion, 'I will not cease until I reach where the two seas meet, or I shall spend an exceptionally long time travelling" ... al-Kahfi 18:60
Allah then informs us that upon meeting Khidr, Moses (as) asked of him:
"May I follow you in order that you may teach me of the knowledge you have been given" ... al-Kahfi 18:66
Details of their venture are related in the Book of Allah and in the well-known hadith of Ubayy ibn Ka'b, which is related by Bukhari and Muslim.
... excerpts taken from The Heirs of the Prophets, ibn Rajab al-Hanbali