Shaykh Uthaymeen rahimahu Allah said:

The mujahid in Allahs cause does not have a greater reward than the student of knowledge if he is killed in the battle field for the sake of Allah 'aza wa jal. He does not have the best reward. And this was pointed out by the scholar Ibn Qayim rahimahu Allah, that if a person specialised in a characteristic that does not mean he has the best reward. The shaheed he characterized in the jihad for the sake of Allah. But under the hand of the student of knowledge and the ulama is a maslaha (rectifying) the ummah and spreading the dawah that would not be in the shaheed account. Have you not seen how much Shaykh al islam ibn Taymiya benefited the ummah? If you took a big number of mujahideen you will not find what has been brought of benefit for the ummah like the knowledge of shaykh al islam ibn Taymiya rahimahu Allah over all of them.

Taken from the majmuu al fatawa of Shaykh Saleh Ibn Uthaymin rahimahu Allah. Fatwa number 25/306-307

Al Imam Saadi Rahimahullah mentioned in his commentary on the book Umdatul Ahkaam page 709

"And it is befitting that it is known that seeking knowledge is more virtous than it (Jihad) particularly in these times in which the scholars have become few, and in which the people have become engaged with the world. So the pursuit in seeking knowledge, then the scholars have mentioned that it is more virtous than many of the acts of worship, rather, than most of it (acts ofworship), and that is in a time of it shining and abundance of the scholars andexcess of that in those times. So then how about in our times in which it doesnot remain in it from knowledge except a little, and no sooner its banners may be wiped out, so then no doubt that seeking knowledge is more virtuous than fighting in the path of Allah, because with it is the correcting of the world, and who ever accepts upon seeking it and its acquisition, and the research in regards to its matters, then he has undertaken a great matter, and a worship, that no doubt is in this day more virtues than fighting in the path of Allah, and (more virtuous) than the prayer, and the fasting, and the hajj, and from the remaining acts of worship unrestrictedly, so if he researches he is in worship, and if he learns knowledge, or travels to seek it, or leaves to its sittings, or ponders in regards to the affairs (of knowledge), then he is in worship and the time of the one learning all of it is worship and Allah knows best