Surah 90. Al-Balad, Ayah 9

I.e., to recognize and to voice the truth of God's existence or, at least, to ask for guidance.

The eyes give us the faculty of seeing, and may be taken in both the literal and the metaphorical sense. In the same way the tongue gives us the faculty of tasting in both senses. Along with the lips, it also enables us to speak, to ask for information and seek guidance, and to celebrate the praises of Allah.