Hadith 7:9
Anas reported God’s messsenger as saying, “Supplication is the pith of worship.” Tirmidhi transmitted it.
وَعَنْ أَنَسٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «الدُّعَاءُ مُخُّ الْعِبَادَةِ» . رَوَاهُ التِّرْمِذِيّ
Original Reference: Mishkat al-Masabih 2231