Blessing on the Prophet, and its Excellence - Section 3 Mishkat al-Masabih 938
Arabic hadith text
وَعَنْ عُمَرَ بْنِ الْخَطَّابِ رَضِيَ اللَّهُ عَنْهُ قَالَ: إِنَّ الدُّعَاءَ مَوْقُوفٌ بَيْنَ السَّمَاءِ وَالْأَرْضِ لَا يَصْعَدُ مِنْهُ شَيْءٌ حَتَّى تُصَلِّيَ عَلَى نبيك. رَوَاهُ التِّرْمِذِيّ
Translation
‘Umar b. al-Khattab said, “The supplication is stopped between heaven and earth, none of it ascending till you invoke blessing on your Prophet.” Tirmidhi transmitted it.