"Jealousy is the worst of evils, because it hurts first one’s friend. " ~~ Moshe Ben Ezra
"A friend will prove himself in time of trouble." ~~ Moses Ibn Ezra
"Who is the greatest of heroes? He that makes his foe his friend." ~~ Avot Derabbi Nathan
"Question a friend: perhaps he did not say what you think, or if he did, so that he will not say it again." ~~ Ben Sira
"Who bears false witness against his friend deserves to be thrown to the wolves." ~~ Talmud, Pesachi
"Those who have wept and laughed together are no longer strangers." ~~ Max Nordau
"No man knows what is in his friend’s heart." ~~ Talmud, Pesachim
"If you do not pity your friend, nobody will pity you." ~~ Tanchuma
"Your enemies you have to take, wherever and however you find them; but fortunately, I can choose my friends. " ~~ Arthur Schnitzler
"Friendship is like a treasury: you cannot take from it more than you put into it." ~~ Benjamin Mandelstamm
"Faithful are the words of a friend; but the kisses of an enemy are deceitful. " ~~ Proverbs (Mishle) 27:6
"Press not your friend to dine with you when you know that he dines not, nor offer him many gifts when you know that he accepts them not! " ~~ Talmud, Chullin