لَسْتُ بِرَايءِحٍ حَتَّى أُفَوِّجَ

means [I am not going in the evening] until I refresh myself by the coolness of the air. (K: there explained by the words أَىْ أُبَرِّدَ عَنْ نَفْسِى [in which, for أُبَرِّدَ, I read أُبْرِدَ]: in some copies [erroneously] عَلَى نفسى.)