I know in Islam we shouldn't assume muslims do bad things and rather think positively but one Muslim girl went out with her non-Muslim friend (also female) for her friend's 18th birthday to a bar and it seemed in the video that the Muslim girl had a drink now my question is, shod I not assume that what she is drinking is alcohol knowing that she is in a bar and celebrating a friends 18th birthday and that she is also eligible to drink in the country? Or am I to assume it is a non-alcoholical beverage?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, sallallaahu`alayhi wa sallam, is His slave and messenger.

There is no doubt that all the affairs of the Muslim should be understood in light of good assumption, meaning that Muslims should not have bad assumption about each other unless there is evidence. Allah, the Exalted, says (what means): {O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin.} [Quran, 49:12]

It is also recorded in the two Saheehs on the authority of Abu Hurayrah that the Messenger of Allah said, “Beware of suspicion, for suspicion is the worst of false tales.”

This Muslim woman’s presence in a bar does not necessarily mean that she drinks wine. So, as long as the matter is based on probability, it should be understood in light of good assumption. In hisShuʿab Al-Iman, Imam Al-Bayhaqi narrated on the authority of Saʿeed ibn Al-Musayyeb that he said, “Some of my brothers of the companions of the Messenger of Allah wrote to me to think good of your Muslim brothers and not to think bad of a word uttered by a Muslim as long as there is a possibility to explain it in light of good assumption.”

However, this Muslim woman had committed a sin by going to this place, and she is sinful since it is impermissible for a Muslim to go to such places of evil unless for a valid reason, such as denying the actions committed therein. Imam Ahmed and Imam At-Tirmidhi narrated on the authority of Jaabir that the Prophet said, “Whoever believes in Allah and the Last Day, let him not sit at a table where alcohol is being passed around …” By this act, this woman has put herself in the position of accusation while a Muslim is required to keep away from placing himself under accusations. The previously mentioned report adds, “Whoever places himself in positions of accusations, let him blame none but himself.”

This means that he is the one who brought upon this sin; it does not mean that others are not blamed for having bad thoughts about him.

Allah knows best.