A search for a very light Higgs boson decaying into a pair of tau leptons is presented within the

framework of the next-to-minimal supersymmetric standard model(NMSSM). This search

is based on a data set corresponding to an integrated luminosity of 19.7 fb^-1 and 2.5 fb^-1

of proton-proton collisions collected by the CMS experiment at a centre-of-mass energy of

8 TeV and 13 TeV respectively. The signal consists of the production of either of the two

lightest scalars, h1 or h2, via gluon-gluon fusion and subsequent decay into a pair of the

lightest Higgs bosons, a1 or h1. The h1 or h2 boson is identified with the observed state

at a mass of 125 GeV. The analysis searches for decays of the a1(h1) states into pairs of tau

leptons and covers a mass range for the a1(h1) boson of 4 to 15 GeV. The search reveals

no significant excess in data above standard model background expectations, and an upper

limit is set on the signal production cross section times branching fraction as a function of

the a1(h1) boson mass.