Bahá’u’lláh wrote:

“…Ye were created to show love one to another and not perversity and rancour. Take pride not in love for yourselves but in love for your fellow-creatures. Glory not in love for your country, but in love for all mankind…”
(Tablets of Bahá’u’lláh, p. 138)

“…Of old it hath been revealed: “Love of one’s country is an element of the Faith of God.”  The Tongue of Grandeur hath, however, in the day of His manifestation proclaimed: “It is not his to boast who loveth his country, but it is his who loveth the world.”
(Gleanings from the Writings of Bahá’u’lláh, p. 95)

“…That one indeed is a man who, today, dedicateth himself to the service of the entire human race. The Great Being saith: Blessed and happy is he that ariseth to promote the best interests of the peoples and kindreds of the earth. In another passage He hath proclaimed: It is not for him to pride himself who loveth his own country, but rather for him who loveth the whole world. The earth is but one country, and mankind its citizens.”
(Gleanings from the Writings of Bahá’u’lláh, p. 250)

“…Ye dwell in one world, and have been created through the operation of one Will. Blessed is he who mingleth with all men in a spirit of utmost kindliness and love.”
(Gleanings from the Writings of Bahá’u’lláh, p. 334)

“…The most glorious fruit of the tree of knowledge is this exalted word: Of one tree are ye all the fruit, and of one bough the leaves. Let not man glory in this that he loveth his country, let him rather glory in this that he loveth his kind…”
(Tablets of Bahá’u’lláh, p. 127-128)

“O ye men of wisdom among nations! Shut your eyes to estrangement, then fix your gaze upon unity. Cleave tenaciously unto that which will lead to the wellbeing and tranquillity of all mankind. This span of earth is but one homeland and one habitation.”
(Tablets of Bahá’u’lláh, p. 67)