Is Surah Ya-Sin/یس the heart of Quran?

**Is Surah یس (Ya-Sin) the heart of the holy Quran?** Perhaps it is considered as a famous sentence or belief that Surah Ya-Sain as Surah 36 of the holy Quran counted as the heart of the noble Quran. I can remember that someday I saw it as a hadith from Imam Jafar-al-Sadiq (a.s.), but I am not certain if he said that. In other word, I am looking for the source of this famous sentence that > Surah Ya-Sin is considered as the heart of the holy Quran.