It is narrated in Bihar al-Anwar that when the Commander of the Faithful, Ali (AS) used to start performing his ablution, the colour of his face would change due to the fear of Allah, most High.
كانَ أميرُ المؤمنينَ (عَلَيهِ الّسَلامُ) إذا أخَذَ في الوُضُوءِ يَتَغَيَّرُ وَجهُهُ مِن خِيفَةِ اللّهِ تعالى .