What is the ruling on a shirt and trousers? Thank you.

A Muslim must cover his 'awra (private parts) with something that does not describe it. The garment beloved to the Prophet, may Allah bless him and grant him peace, was a long and ample qamis (tunic), which is better for covering than an izar (waist wrap) and a rida' (upper garment). There is no harm in wearing the shirt known today or trousers, as long as they do not describe the 'awra or are made of silk.