Wahb bin Munabbih (may Allah have mercy on him) said: The bribe in which the giver is sinful is not that he gives it to protect his wealth and his life; he is not sinful in that. The bribe in which a person is sinful is the one given to take what is someone else's right.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20483