Mas is a great song, but whoever wrote the bass part got lazy, 'cause it only has four
notes in it.  I feel like I'm cheating by even calling this a tab, but here it is.

G:--------6---------6:
D:----6-9-------6-9--:
A:--4-------4-4------:
E:-------------------:

The same baseline can also be played with this fingering:

G:----1-4-6-----1-4-6--:
D:---------------------:
A:--4-------4-4--------:
E:---------------------:

Or:

G:--------6---------6--:
D:----6-9-------6-9----:
A:---------------------:
E:--9-------9-9--------:

I'm not sure which is easier.

The bass just repeats this pattern through the whole song.  There are a few measures 
when it rests, listen to the cd for those parts and to get the rhythm down.
I found the fingering for this a little awkward at first, but it just takes repitition 
to get it down, and it's really easy after that.  Maybe it would be better if it were in 
a different tuning, but I kept mine at the standard GDAE.
Have fun!