Bhikkhus, whatever kinds of worldly merit there are, all are not worth one 16th part of the release of mind by universal friendliness; in shining, glowing, beaming & radiance the release of mind by universal friendliness far excels & surpasses them all. Itivuttaka 27

As a mother even with own life protects her only child, so should one cultivate immeasurable loving-kindness towards all living beings. The Metta Sutta

He who both day and night takes delight in harmlessness sharing love with all that live, finds enmity with none.
Samyutta Nikaya. I, 208

What are the eleven advantages of Metta ?

One sleeps Happy!
One wakes Happy!
One dreams no evil dreams!
One is liked and loved by all human beings!
One is liked and loved by all non-human beings too!
One is Guarded & Protected by the divine Devas!
One cannot be Harmed by Fire, Poison, or Weapons!
One swiftly Attains the Concentration of Absorption!
One’s appearance becomes Serene, Calm, & Composed!
One dies without Confusion, Bewilderment, or Panic!
One reappears after death on the Brahma level if one has penetrated to no higher level in this very life!
Anguttara Nikaya XI.16

They may address you in an affectionate way or a harsh way. They may address you in a beneficial way or an unbeneficial way. They may address you with a mind of good-will or with inner hate. In any event, you should train yourselves: ‘Our minds will be unaffected and we will say no evil words. We will remain sympathetic to that person’s welfare, with a mind of good will, and with no inner hate. We will keep pervading him with an awareness imbued with good will and, beginning with him, we will keep pervading the all-encompassing world with an awareness imbued with good will equal to the great earth — abundant, expansive, immeasurable, free from hostility, free from ill will.’ That’s how you should train yourselves.
Majjhima Nikaya 21

When one gives birth to hatred for an individual, one should direct one’s thoughts to the fact of his being the product of his actions: ‘This venerable one is the doer of his actions, heir of his actions, born of his actions, related by his actions, and is dependent on his actions. Whatever actions he does, for good or for evil, to that will he fall heir.’ Thus the hatred for that individual should be subdued.
Anguttara Nikaya V.161

I have good will for footless beings,
good will for two-footed beings,
good will for four-footed beings,
good will for many-footed beings.

May footless beings do me no harm.
May two-footed beings do me no harm.
May four-footed beings do me no harm.
May many-footed beings do me no harm.

May all creatures,
all breathing things,
all beings — each & every one –
meet with good fortune.
May none of them come to any evil.
Anguttara Nikaya IV.67

The disciple of the Noble Ones, who in this way is devoid of coveting, devoid of ill will, undeluded, clearly comprehending and mindful, dwells, having pervaded, with a mind of lovingkindness, one quarter; likewise the second; likewise the third; likewise the fourth; so above, below, and across; he dwells, having pervaded because of the existence in it of all living beings, everywhere, the entire world, with the great, exalted, boundless thought of amity that is free of hate or malice.

He lives, having pervaded, with a mind of compassion, one quarter; likewise the second; likewise the third; likewise the fourth; so above, below, and across; he dwells, having pervaded because of the existence in it of all living beings, everywhere, the entire world, with the great, exalted, boundless thought of compassion that is free of hate or malice.

He lives, having pervaded, with a mind of joy, one quarter; likewise the second; likewise the third; likewise the fourth; so above, below, and across; he dwells, having pervaded because of the existence in it of all living beings, everywhere, the entire world, with the great, exalted, boundless thought of gladness that is free of hate or malice.

He lives, having pervaded, with a mind of equanimity, one quarter; likewise the second; likewise the third; likewise the fourth; so above, below, and across; he dwells, having pervaded because of the existence in it of all living beings, everywhere, the entire world, with the great, exalted, boundless thought of equanimity that is free of hate or malice.

Kalama Sutta, Anguttara Nikaya 3.65

“There are these five ways of subduing hatred by which, when hatred arises in a monk, he should wipe it out completely. Which five?

“When one gives birth to hatred for an individual, one should develop good will for that individual. Thus the hatred for that individual should be subdued.

“When one gives birth to hatred for an individual, one should develop compassion for that individual. Thus the hatred for that individual should be subdued.

“When one gives birth to hatred for an individual, one should develop equanimity toward that individual. Thus the hatred for that individual should be subdued.

“When one gives birth to hatred for an individual, one should pay him no mind & pay him no attention. Thus the hatred for that individual should be subdued.

“When one gives birth to hatred for an individual, one should direct one’s thoughts to the fact of his being the product of his actions: ‘This venerable one is the doer of his actions, heir to his actions, born of his actions, related by his actions, and has his actions as his arbitrator. Whatever action he does, for good or for evil, to that will he fall heir.’ Thus the hatred for that individual should be subdued.

“These are five ways of subduing hatred by which, when hatred arises in a monk, he should wipe it out completely.”

Aghatavinaya Sutta (Anguttara Nikaya, 5.161)

For one who mindfully develops
Boundless loving-kindness
Seeing the destruction of clinging,
The fetters are worn away.

If with an uncorrupted mind
He pervades just one being
With loving kindly thoughts,
He makes some merit thereby.

But a noble one produces
An abundance of merit
By having a compassionate mind
Towards all living beings.

Those royal seers who conquered
The earth crowded with beings
Went about performing sacrifices:
The horse sacrifice, the man sacrifice,
The water rites, the soma sacrifice,
And that called “the Unobstructed.”

But these do not share even a sixteenth part
Of a well cultivated mind of love,
Just as the entire starry host
Is dimmed by the moon’s radiance.

One who does not kill
Nor cause others to kill,
Who does not conquer
Nor cause others to conquer,
Kindly towards all beings —
He has enmity for none.

Source: http://www.wildmind.org