Hadithcore
Mishkat al-Masabih, 936

Ruwaih' reported God’s Messenger as saying, “If anyone invokes a blessing on Muhammad saying, ‘O God, cause him to occupy the place near You on the day of resurrection’, he will be guaranteed my intercession.” Ahmad transmitted it.

وَعَن رويفع أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: مَنْ صَلَّى عَلَى مُحَمَّدٍ وَقَالَ: اللَّهُمَّ أَنْزِلْهُ الْمَقْعَدَ الْمُقَرَّبَ عِنْدَكَ يَوْمَ الْقِيَامَةِ وَجَبَتْ لَهُ شَفَاعَتِي ". رَوَاهُ أَحْمد

References1 variant
In-Book Reference
Book 4, Hadith 359