If a man aspires towards a righteous life, his first act of abstinence is from injury to animals.
— Albert Einstein
Astonishing Compassion Towards Animals quotations
It is much easier to show compassion to animals. They are never wicked.

Humanity's true moral test, its fundamental test…consists of its attitude towards those who are at its mercy: animals.

The indifference, callousness and contempt that so many people exhibit toward animals is evil first because it results in great suffering in animals, and second because it results in an incalculably great impoverishment of the human spirit.
It ill becomes us to invoke in our daily prayers the blessings of God, the Compassionate, if we in turn will not practice elementary compassion toward our fellow creatures.
As often as Herman had witnessed the slaughter of animals and fish, he always had the same thought: in their behavior toward creatures, all men were Nazis.

Encompass with your mercy and compassion all animals and creatures.
Do not say, "this is inanimate and has no awareness." Indeed, it does; it is you yourself who have no awareness! So let existence be as it is, and be merciful towards it with the mercifulness of the Creator in the midst of His creation.
Have compassion towards each other, including animals.
Love and respect every living being on this planet - a key factor to a greater society.
Kindness and compassion towards all living things is a mark of a civilized society. Conversely, cruelty, whether it is directed against human beings or against animals, is not the exclusive province of any one culture or community of people.
I'm very sceptical about the prospects for 'big' environmental causes - 'saving the planet', halving the world's population, ending the exploitation of animals, and so on - but a person can ask him- or herself how he or she personally may exercise compassion or humility towards animals, vegetal life and so on.
Have compassion towards each other, including animals.
Buddhism cannot be true to itself until Buddhists resolve their ambivalence toward nonhuman animals and extend the full protection of their compassion to the most harmless and helpless of those who live at our mercy in the visible realms.

Let a man fear, above all, me, his God, and so much the gentler will he become toward my creatures and animals, on whom, on account of me, their Creator, he ought to have compassion.
Dominion does not mean domination. We hold dominion over animals only because of our powerful and ubiquitous intellect. Not because we are morally superior. Not because we have a "right" to exploit those who cannot defend themselves. Let us use our brain to move toward compassion and away from cruelty, to feel empathy rather than cold indifference, to feel animals' pain in our hearts.