[16].Surah An-Nahl [The Bees] : Ayat 15-16

Ayat 15. And He has affixed into the earth mountains standing firm, lest it should shake with you, and rivers and roads, that you may guide yourselves.

Ayat 16. And landmarks (signposts, etc. during the day) and by the stars (during the night), they (mankind) guide themselves. 

Hazrat Masruq (May Allah be pleased with him) said: We visited `Abdullah bin Masud (May Allah be pleased with him) and he said to us: O people! He who has the knowledge of any matter may convey it to the others. And he who has no knowledge, thereof, should say: "Allahu a`lam (Allah knows better).'' It is a part and parcel of knowledge that a man who has no knowledge of a matter should say: "Allah knows better.'' Allah said to His Prophet  [SAWW](PBUH): "Say (O Muhammad  [SAWW](PBUH)): `No wage do I ask of you for this (the Qur'an), nor am I one of the Mutakallifun (those who pretend and fabricate things which do not exist).''' (38:86) 

Lesson : as mentioned above in Surah An-Nahl Ayat 15.that you may guide yourselves. If one does not know about something, he should not say anything about it by way of conjecture, speculation and guesswork because this is also pretension which is forbidden. When religious scholars are asked about anything which they do not know, they should confess their ignorance. Such a confession is also a mark of scholarship. In other words, they should abstain from giving verdict about any matter without making a thorough study and research on it.

[Al-Bukhari 06, Chapter 60, Hadith # 333].