MUSE 1D spectra of the multiple images A1+B1, A2+B2, A3+B3, A4+B4, and stacked (top row), extracted within the blue apertures highlighted in Fig. 2. The spectra were smoothed with a ∼ 2.5 Å boxcar filter. We zoom in around five wavelength ranges where we observe the main absorption and emission lines used to confirm the redshift measurement of 1.880. The blue lines represent the observed spectra in units of 10⁻¹⁸ erg s⁻¹ cm⁻² Å⁻¹, and the gray regions indicate the 1σ uncertainties.