Sayyiduna Wathilah bin al-Asqa' (may Allah be pleased with him) narrates that the Prophet (peace and blessings be upon him) said: "Whoever seeks knowledge and attains it, Allah Almighty records for him a double share (kifl) of reward; and whoever seeks knowledge but does not attain it, Allah Almighty records for him a single share of reward."
Tabarani recorded it in al-Mu'jam al-Kabir, and its narrators have been declared trustworthy.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب العلم / 502