What is the ruling on accessing Facebook while seeing pictures of women with uncovered hair?

It is forbidden to access Facebook with the intention of viewing 'awrat (parts of the body that should be covered). However, if one accesses it for a permissible benefit, and then incidentally encounters images of 'awrat, there is no sin upon him. Nevertheless, he must lower his gaze, based on the words of Allah Almighty: (Tell the believing men to lower their gaze) and the words of the Prophet, peace and blessings be upon him: "Do not follow a glance with another glance, for the first is for you but the last is not."

Moreover, Sheikh Ibn Baz mentioned that attending gatherings of evil is permissible if the intention is for the public good and to clarify the harm of evil, not to enjoy it.

A Muslim must be careful not to waste time on social media without real benefit, and to safeguard his religion from the lusts and doubts available therein.