Anas (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: “Whoever goes out to seek knowledge is in the cause of Allah until he returns.”
شرح الحديث :
Anyone who leaves his home or country in search of Shariah knowledge is in the same category of the one who goes out to fight in the cause of Allah, the Almighty, until he returns to his family. Indeed, the knowledge seeker is like a fighter in the cause of Allah in reviving religion, putting the devil to disgrace, and tiring his own soul out in a good cause.