What is the ruling on obtaining a tender knowing that it involves bribery?

It is not permissible for a government engineer to demand a commission for his obligated work, nor is it permissible to pay him one, as this falls under prohibited bribery. This is based on the Prophet, peace and blessings be upon him, who said: "Gifts to officials are a form of embezzlement," and his saying: "The Messenger of Allah, peace and blessings be upon him, cursed the briber and the bribed."

It is also forbidden to consume people's wealth unjustly, as Allah Almighty says: "And do not consume one another's property unjustly or hand it over to the authorities to consume a portion of the property of others sinfully while you know [that it is unlawful]."

However, if your right is contingent upon paying the bribe and you find no alternative, then there is no blame upon you, and the sin falls upon the engineer.