The time-dependent CP asymmetries of B0 → π+π− and B0s → K+K− decays are measured using a data sample of pp collisions corresponding to an integrated luminosity of 1.9 fb−1, collected with the LHCb detector at a centre-of-mass energy of 13 TeV. The results are Cππ=−0.311±0.045±0.015,Sππ=−0.706±0.042±0.013,CKK=0.123±0.034±0.015,SKK=0.164±0.034±0.014,AΔΓKK=−0.83±0.05±0.09, where the first uncertainties are statistical and the second systematic. The same data sample is used to measure the time-integrated CP asymmetries of B0 → K + π− and B0s → K−π+ decays and the results are AB0CP=−0.0824±0.0033±0.0033,AB0sCP=0.236±0.013±0.011. All results are consistent with earlier measurements. A combination of LHCb measurements provides the first observation of time-dependent CP violation in B0s decays.