Section 2 Mishkat al-Masabih 2231
Arabic hadith text
وَعَنْ أَنَسٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «الدُّعَاءُ مُخُّ الْعِبَادَةِ» . رَوَاهُ التِّرْمِذِيّ
Translation
Anas reported God’s messsenger as saying, “Supplication is the pith of worship.” Tirmidhi transmitted it.