ENOfficial
Anas reported God’s messsenger as saying, “Supplication is the pith of worship.” Tirmidhi transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَنْ أَنَسٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «الدُّعَاءُ مُخُّ الْعِبَادَةِ» . رَوَاهُ التِّرْمِذِيّ
sunnah.com