Please could you advise me on the legality of a man to pray with his hair tied back?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

Imaam Muslim reported that Ibn 'Abbaas saw ‘Abdullaah ibn Al-Haarith praying while his hair is knotted in the back, so he went to him and untied his knot. When the man finished his prayer he told Ibn 'Abbaas: “What was wrong with my hair?”, so Ibn ‘Abbaas said: “I heard the Prophet, sallallaahu ‘alayhi wa sallam, saying: “The person who performs the prayer in this condition is like the one who performs the prayer while being handcuffed.”

Moreover, Abu Raafi’ said: “The Prophet prohibited for a man to pray while his hair is knotted.” [Ahmad]

Therefore, it is disliked for a man to perform the prayer while his hair is knotted, but if he prays in this condition, his prayer is valid and he is not obliged to make it up.

Allaah Knows best.