The Quran

وَضَرَبَ اللَّهُ مَثَلًا رَجُلَينِ أَحَدُهُما أَبكَمُ لا يَقدِرُ عَلىٰ شَيءٍ وَهُوَ كَلٌّ عَلىٰ مَولاهُ أَينَما يُوَجِّههُ لا يَأتِ بِخَيرٍ ۖ هَل يَستَوي هُوَ وَمَن يَأمُرُ بِالعَدلِ ۙ وَهُوَ عَلىٰ صِراطٍ مُستَقيمٍ

Muhammad Asad

And God propounds [to you] the parable of two [other] men - one of them dumb,¹ unable to do anything of his own accord, and a sheer burden on his master: to whichever task the latter directs him,² he accomplishes no good. Can such a one be considered the equal of [a wise man] who enjoins the doing of what is right and himself follows a straight way?³

The term abkam signifies "dumb" both in the literal, physiological sense and (as in colloquial English) in the sense of being "unable to speak properly" on account of intellectual weakness: i.e., "dull-witted" or "stupid". Both these meanings are contained in the above Qur'anic description.
Or: "wherever he sends him".
I.e., who is not only wise and righteous but also has the strength and authority to enjoin a righteous way of living upon others. Thus, while in the first parable the main issue is the contrast between freedom and bondage or - more generally - between dependence and independence, in the second parable we are given the antithesis of dumbness and incompetence, on the one hand, and wisdom, justice and competence, on the other; and in both parables the implication is the same (see note 85 above).