For this reason, the law is established which no passion can disturb. It is void of desire and fear, lust and anger. It is mens sine affectu, written reason, retaining some measure of the divine perfection. It does not enjoin that which pleases a weak, frail man; but, without any regard to persons, commands that which is good, and punishes evil in all, whether rich or poor, high or low. It is deaf, inexorable, inflexible.

Algernon Sidney (1623-1683) English politician, republican political theorist [also Sydney]

Discourses Concerning Government, ch. 3, § 15 (1689)
    (Source)

The Latin means "mind without emotion."

John Adams was a huge fan of Sidney (whose republican / anti-monarchical writings against King Charles II, leading to his execution, had significant impact on many of the Founders). Adams incorporated the above speech into the closing arguments of his legal defense of the British soldiers in the Boston Massacre trials (1770-12-04). Because of that use, Adams is often cited for the above quote, though he clearly attributed it to Sidney.

To the above, Adams added this, the last line of his closing:

On the one hand it is inexorable to the cries and lamentations of the prisoners; on the other it is deaf, deaf as an adder to the clamours of the populace.