Is absence from medical internship, where no scientific benefit is gained, considered unlawful (haram), making the earned salary unlawful (haram)? And is signing the attendance sheet on behalf of an absent person considered bearing false witness? Does the ruling differ if the absent person is ill or has an excuse?

It is not permissible to sign the attendance sheet on behalf of absent colleagues, as this involves lying, deception, and a betrayal of trust. The salary for days of absence is not lawful for the absent individual, because they did not fulfill their employment contract. This constitutes unlawful acquisition of wealth. What was taken must be returned to the employer if possible; otherwise, it should be given as charity. As for absence due to illness or a valid excuse, the work regulations and contract terms apply.