Shaheen-3 and Ababeel use the same warhead.
Shaheen-3 carries one and Ababeel carries three of the same warhead.
The warhead is a strategic yield fission fusion device which is about 0.74 meter wide and 2 meter tall.
Fitting three of these in the Ababeel warhead casing which is 3.4 meters tall and 1.8 metres wide.
In fact Pakistan can fit 4 Shaheen-3 warheads on ababeel. But then weight will be an issue.
Currently the Shaheen-3 carries a 500 kg warhead to a distance of 2750 km.
Ababeel carries three such warheads weighing 1.5 tons to a distance of 2200 km.
Hence paying penalty of carrying excess weight in reduced range.