بُلُوغُ الْمَرَامِ
Bulugh al-Maram 427
The Book of Prayer
وَعَنْ اِبْنِ عُمَرَ قَالَ: قَالَ رَسُولُ اَللَّهِ - صلى الله عليه وسلم -{ صَلُّوا عَلَى مَنْ قَالَ: لَا إِلَهَ إِلَّا اَللَّهُ, وَصَلُّوا خَلْفَ مَنْ قَالَ: لَا إِلَهَ إِلَّا اَللَّهُ } رَوَاهُ اَلدَّارَقُطْنِيُّ بِإِسْنَادٍ ضَعِيفٍ . [1] .
Narrated Ibn 'Umar (RA): Allah's Messenger (ﷺ) said: "Pray (funeral prayers) over him who said (believed): 'Nothing deserves to be worshiped except Allah'; and pray behind him who says: 'Nothing deserves to be worshiped except Allah'." [ad-Daraqutni reported it through a weak chain of narrators].
Sunnah.com reference: Book 2, Hadith 334