سنن ابن ماجه

It was narrated that Ibn 'Umar said: "I saw the Messenger of Allah (ﷺ) in his (constructed) toilet, facing towards the Qiblah." (Da'if) (One of the narrators) 'Eisa said: "I told that to Sha'bi, and he said: 'Ibn 'Umar spoke the truth. As for the words of Abu Hurairah, he said: "In the desert do not face the Qiblah nor turn one's back towards it." As for the words of Ibn 'Umar, he said: "In the (constructed) toilet there is no Qiblah so turn in whatever direction you want." Another chain with similar wording.