عَنِ النُّعْمَانِ بْنِ بَشِيرٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «الدُّعَاءُ هُوَ الْعِبَادَةُ» ثُمَّ قَرَأَ: (وَقَالَ رَبُّكُمُ ادْعُونِي أَسْتَجِبْ لَكم) رَوَاهُ أَحْمَدُ وَالتِّرْمِذِيُّ وَأَبُو دَاوُدَ وَالنَّسَائِيُّ وَابْنُ مَاجَه
Translation
‘Umar b. al-Khattab said

I asked the Prophet’s permission to perform an ‘umra and he gave me permission, saying, “Include me in your supplication, little brother, and do not forget me.” Then he said a word to me for which I would not be willing to take the world in exchange. Abu Dawud and Tirmidhi transmitted it, Tirmidhi’s version ending with “do not forget me.”