The Qur'an warns about speaking without knowledge:
And do not pursue that of which you have no knowledge. Indeed, the hearing, the sight and the heart - about all those [one] will be questioned. -- Qur'an 17:36
One of my Muslim friends uses this as a reason to avoid speaking about Islam almost entirely, and encourages others to likewise avoid talking about Islam. He seems fearful that he might be punished for inaccuracies in statements he makes.
I'm not sure what to make of his approach. On one hand, it's good to be cautious, but maybe this is going too far. After all, surely talking about Islam is necessary to learn about Islam.
Question: Are we encouraged to talk about Islam, or should we be cautious to avoid talking without knowledge?
I'm not seeking a judgement on his approach, but seeking the relevant material from the Qur'an and Sunnah.