Flame retardant for textiles contg. cellulose consists of an aq. soln. of a condensate (I) of tetrakis(hydroxymethyl)phosphonium sulphate (II) and urea. (I) pref. contains 4.0-9.0 esp. 5-7.5 (wt.)pts. (II)/pt. urea and the soln. contains 8.0-10.0% P. The use of the sulphate instead of the chloride avoids the possibility of the formation of bis(chloromethyl)ether, which is very toxic. The use of the precondensate of (II) and urea reduces the amt. of HCHO, which is partly eliminated during drying. In an example, (I) was prepd. by reacting 1.32 mole (II) and 1.65 mole urea in aq. soln., followed by treatment with dil. H peroxide soln. The (II)/urea wt. ratio of (I) was 5.4:1.