The believers who failed to join the Ghazwa of Badr and those who took part in it are not equal (in reward).
Sahih al-Bukhari Book 64, Hadith 6
← Previous Hadith On the day of the battle of Badr, the Prophet (ﷺ) said, "O Allah! I appeal to You (to fulfill) Your Covenant and Promise. O Allah! If Your Will is that none should worship You (then give victory to the pagans)." Then Abu Bakr took hold of him by the hand and said, "This is sufficient for you." The Prophet came out saying, "Their multitude will be put to flight and they will show their backs." (54.45)

Sahih al-Bukhari Book 64, Hadith 5 Next Hadith → I and Ibn `Umar were considered too young to take part in the battle of Badr.

Sahih al-Bukhari Book 64, Hadith 7