The instant invention relates to a textile article comprising a flame-retardant treated fabric including an oxidized polymer obtained from an ammonia curing of a condensate of (i) a tetrakis (hydroxyorgano) phosphonium salt; and (ii) urea or thiourea; followed by an oxidation into phosphine oxide groups of at least one part of the phosphonium groups present on the cured condensate, wherein said flame-retardant treated fabric: —is intended to be used as a stable substrate in which the formation of formaldehyde over the time is inhibited; and —contains less than 1% by weight of phosphorus present in phosphonium groups, based on the total weight of the flame-retardant treated fabric.