https://islamqa.info/en/answers/142577/how-could-the-shaytaan-appear-to-the-disbelievers-in-the-battle-of-badr-when-he-is-chained-up-during-ramadan-and-the-battle-was-in-ramadan

Praise be to Allah.

Firstly: 

It is well-known in the books of tafseer and seerah that the Shaytaan was present at the battle of Badr and that he appeared in the form of Suraaqah ibn Maalik. That is mentioned in the commentary on the verse in which Allah, may He be exalted, says (interpretation of the meaning):

“And (remember) when Shaitan (Satan) made their (evil) deeds seem fair to them and said, ‘No one of mankind can overcome you this day (of the battle of Badr) and verily, I will be your protector.’ But when the two forces came in sight of each other, he ran away and said ‘Verily, I have nothing to do with you. Verily! I see what you see not. Verily! I fear Allah for Allah is Severe in punishment.’”

[al-Anfaal 8:48].

How could the Shaytaan appear to the disbelievers in the battle of Badr when he is chained up during Ramadan and the battle was in Ramadan?