Translation of the verse 18 from Surah Az-Zumar : Number of verses 75 - - page 460 - Part 23.
Those who listen to the Word [good advice La ilaha ill-Allah (none has the right to be worshipped but Allah) and Islamic Monotheism, etc.] and follow the best thereof (i.e. worship Allah Alone, repent to Him and avoid Taghut, etc.) those are (the ones) whom Allah has guided and those are men of understanding (like Zaid bin 'Amr bin Nufail, Salman Al-Farisi and Abu Dhar Al-Ghifari). [Tafsir Al-Qurtubi, Vol. 12, P. 244]
Who listen to speech and follow the best of it. Those are the ones Allah has guided, and those are people of understanding.
(39:18) to those who pay heed to what is said and follow the best of it. *36 They are the ones whom Allah has guided to the Right Way; they are the ones endowed with understanding.
*36) This verse can have two meanings: (1) That they do not follow every voice but ponder over what every man says and accept only what is right and true; and (2) that they do not try to give a false meaning to what they hear but adopt its good and righteous aspects.