From "On the Harmony of Religions and Philosophy." In Arabic, "Kitab fasl al-maqal":
For when a man sees the sun, the moon, and all the stars, which are the cause of the four seasons; of days and nights, of rain, water and winds, of the inhabitation of the parts of the earth, of the existence of man, and of the being of all the animals and the plants and of the earth being fit for the habitation of a man, and other animals living in it; and the water fit for the animals living in it; and the air fit for birds, and if there be anything amiss in this creation and edifice, the whole world would come to confusion and disorder, then he would come to know with certainty that it is not possible that this harmony in it for the different members of the universe -- man, animals, and plants -- be found by chance only.
He will know that there is one who determined it, and so one who made it by intention, and that is God, exalted and magnified may He be. He would know with certainty that the universe is a created thing, for he would necessarily think that it is not possible that in it should be found all this harmony, if it be not made by someone, and had come into existence by chance alone. This kind of argument, is quite definite and at the same time clear, and some have mentioned it here. It is based upon two principles which are acknowledged by all. One of them being, that the universe, with all its component parts, is found fit for the existence of man and things; secondly, that which is found suitable in all its parts, for a single purpose, leading to a single goal, is necessarily a created thing. So those two principles lead us naturally to admit that the universe is a created thing, and that there is a maker of it. Hence "the argument of analogy" leads to two things at one and the same time, and that is why it is the best argument for proving the existence of God. This kind of reasoning is also found in the Qur'an in many verses in which the creation of the universe is mentioned.
For instance, "Have We not made the earth a bed, and the mountains for shelter to fix the same? And have We not created you of two sexes; and appointed your sleep for rest and made the night a garment to cover you, and destined the day to a gaining of a livelihood; and built over you seven heavens, and placed therein a burning lamp? And do We not send down from the clouds pressing forth rain, water pouring down in abundance, that We may hereby produce corn and herbs, and gardens planted thick with trees" [Qur'an 77.3ff]. If we ponder over this verse it would be found that our attention has been called to the suitability of the different parts of the universe for the existence of man. In the very beginning we are informed of a fact well-known to all -- and that is that the earth has been created in a way which has made it suitable for our existence. Had it been unstable, or of any other shape, or in any other place, or not of the present proportion, it would not have been possible to be here, or at all created on it. All this is included in the words, "Have We not made the earth a bed for you"? for in a bed are collected together all the qualities of shape, tranquility, and peace, to which may be added those of smoothness and softness.
Then He tells us of the advantage of the sun for those living on the earth and says, "And placed therein a burning lamp. " He calls it a lamp because in reality it is all darkness, and light covers the darkness of the night, and if there be no lamp, man can get no advantage out of his sense of sight at nighttime; and in the same way if there were no sun the animals can have no benefit of their sense of seeing. He calls our attention to this advantage of the suns ignoring others because it is the noblest of all the advantages and the most-apparent of all. Then He tells us of His kindness in sending down rain, for the sake of the plants and the animals. The coming down of rain in an appointed proportion, and at an appointed season, for the cultivated fields cannot be by chance alone, but is the result of divine solicitude for us all. So He says, "And do We not send down from the clouds pressing forth rain, water pouring down in abundance that We may hereby produce corn and herbs, and gardens planted thick with trees."
There are many verses of the Qur'an on this subject. For instance, He says, "Do you not see how God has created the seven heavens, one above another, and has placed the moon therein for a light, and has appointed the sun for a taper? God has also provided and caused you to bring forth wheat from the earth" [Qur'an 71.14-16]. If we were to count all such verses and comment upon them showing the kindness of the Creator for the created, it would take too many volumes. We do not intend to do it in this book. If God should grant us life and leisure we shall write a book to show the kindness of God to which He has called our attention.""""