Many days had not elapsed after this event, when one morning Mazin and the sisters sitting together in a gallery of the palace, observed a thick cloud of dust rising from the desert and approaching towards them.  As it came nearer they perceived through it a troop of horsemen; upon which the sisters, desiring Mazin to retire into an inner chamber, went to the gateway to inquire who the strangers might be.  They were servants of the genie sultan, father to the ladies, and sent by him to conduct them to his presence, in order to attend the nuptials of a near relation.  Upon this summons the sisters prepared for the journey, and at the end of three days departed, assuring Mazin that they would return in a month.  At taking leave they gave him the keys of every apartment in the palace, telling him that he might open every door except one, which to enter might be attended with unpleasant consequences, and therefore had better be avoided.  Mazin promised to observe their caution; and for many days was so well amused in examining the magnificent rooms and curiosities of the palace, that he did not feel a wish to transgress till the forbidden door alone remained unopened.  Having then nothing to divert him, he could not resist the impulse of curiosity, but unlocked the door, which opened on a marble staircase by which he ascended to the terraced roof of the palace, from whence a most delightful prospect feasted his sight.  On one side his eye was arrested by an extensive garden, in the centre of which, under shady trees, was a basin of clear water, lined with gems of every colour and description.  He resolved to visit this enchanting object; and descending the staircase, explored his way through a long arcade, which led him at length into the garden, in which he diverted himself with the scenery it afforded for some time.  He then retired to an alcove on the margin of the basin, and sat down; but had not rested many moments, when to his astonishment he beheld descending from the sky a company of beautiful damsels, whose robes of light green silk floating in the air seemed their only support.  Alarmed at such a preternatural appearance, he retired to the end of the alcove, from whence he watched their motions.  They alighted on the brink of the water, and having thrown off their robes, stood to the enraptured view of Mazin in native loveliness.  Never had he beheld such enchanting beauty; but one even more exquisitely charming than the rest attracted his gaze, and from the instant fixed the affections of his heart.  They now plunged into the basin, where for some time they amused themselves by swimming, every now and then playfully dashing the water over themselves and at each other.  When satiated with frolic they came out of the water, sat for some time on the verdant margin, then dressed themselves, and adjusting their robes to the air, soared aloft, and were soon far from the sight of the enamoured Mazin, who followed them till his eyes could stretch no farther; then despairing of ever again beholding the object of his affections, he fainted on the grass, and it was some time before he recovered his senses.  He returned melancholy to the palace, and spent the night in reposeless agitation.