Muwatta Malik #739
Hajj
The Arabic includes the chain of narration (sanad) and the collector's commentary; the English translation shows the Prophet's words only.
وَحَدَّثَنِي مَالِكٌ، عَنْ حُمَيْدِ بْنِ قَيْسٍ، عَنْ عَطَاءِ بْنِ أَبِي رَبَاحٍ، أَنَّ عُمَرَ بْنَ الْخَطَّابِ، قَالَ لِيَعْلَى ابْنِ مُنْيَةَ وَهُوَ يَصُبُّ عَلَى عُمَرَ بْنِ الْخَطَّابِ مَاءً وَهُوَ يَغْتَسِلُ اصْبُبْ عَلَى رَأْسِي . فَقَالَ يَعْلَى أَتُرِيدُ أَنْ تَجْعَلَهَا بِي إِنْ أَمَرْتَنِي صَبَبْتُ . فَقَالَ لَهُ عُمَرُ بْنُ الْخَطَّابِ اصْبُبْ فَلَنْ يَزِيدَهُ الْمَاءُ إِلاَّ شَعَثًا .
Malik related to me from Humayd ibn Qays from Ata ibn Abi Rabah
that 'Umar ibn alKhattab once asked Yala ibn Munya, who was pouring
out water for him while he was having a ghusl, to pour some on his
head. Ya'la said, "Are you trying to make me responsible? I will only
pour it out if you tell me to do so." Umar ibn al-Khattab said, "Pour.
It will only make (my head) more unkempt."
About Muwatta Malik
This hadith is #739 from Muwatta Malik, in the Book of Hajj.