It is said that arahants never dream. What are the textual sources for this claim?
Dreams are not mentioned a lot int he suttas. Perhaps you can search the vinaya instead of the suttas.
THe best there is for the suttas is ''the lack of evil dreams'', from metta


  "Monks, eleven advantages are to be expected from the release
  (deliverance) of heart by familiarizing oneself with thoughts of
  loving-kindness[1], by the cultivation of loving-kindness, by
  constantly increasing these thoughts, by regarding loving-kindness as
  a vehicle (of expression), and also as something to be treasured, by
  living in conformity with these thoughts, by putting these ideas into
  practice, and by establishing them. What are the eleven?
  
  "He sleeps in comfort. He awakes in comfort He sees no evil dreams.
  http://obo.genaud.net/dhamma-vinaya/ati/an/11_elevens/an11.016.piya.ati.htm


there is the same thing with mindfulness http://obo.genaud.net/dhamma-vinaya/pts/an/05_fives/an05.210.hare.pts.htm

In the suttanipata, the buddha says dreams are worthless, contrary to what puthujjanas believe


  Who has destroyed (belief) in omens, in luck, the occurrence of dreams
  and other signs such, who is rid of the bane of what is auspicious,
  such a one rightly would wander in the world.


https://www.dhammatalks.org/suttas/KN/StNp/StNp2_13.html


  Whoso ’mong them strong efforts made resembling Brahma, best, he never
  did engage in sex not even in a dream.
  https://www.dhammatalks.org/suttas/KN/StNp/StNp2_7.html
  
  One of my followers would not cast spells, Or interpret dreams, Nor
  would they practice astrology, Prognosticate animal sounds,
  https://www.dhammatalks.org/suttas/KN/StNp/StNp4_14.html