In the course of our 870μm APEX/LABOCA follow up of the Herschel Lensing Survey we have detected a source in AS1063, that has no counterparts in any of the Herschel PACS/SPIRE bands, it is a Herschel drop-out with S 870/S 500 ≥0.5. The 870μm emission is extended and centered on the brightest cluster galaxy suggesting a multiply imaged source. Based on the observed properties and on our lens model we find that this source could be the first SMG with a moderate far infrared luminosity (LFIR < 1012L ) detected so far at z > 4. In deep HST observations we identified a multiply imaged z∼6 source and we measured its spectroscopic redshift z = 6.107 with VLT/FORS. This source could be associated with the SMG but it is most likely offset spatially by 10-30 kpc and they could be two interacting galaxies. With a FIR luminosity in the range [5 − 15] × 1011L corresponding to a star formation rate in the range [80 − 260] M yr−1, this SMG would be more representative than the extreme starbursts usually detected at z > 4. With a total magnification of ∼25 it would therefore open a unique window to the ’normal’ dusty star forming galaxies at the end of the epoch of reionization. Alternatively the 870μm emission could be substructures in the Sunyaev-Zel’dovich effect due to shocked gas in the merging cluster.