Shiva Purana
अंगुलीनां च रंध्रेण लंबं पश्येद्दिवाकरम् । आत्मप्रदक्षिणं कृत्वा शुद्धाचमनमाचरेत् २८ ।
In the midday the sun is to be viewed through the fingers reciting the mantra prescribed for that. The circumambulation of oneself is performed (in the prescribed manner) and the pure Ācamana (without mantras) is performed.
english translation
aMgulInAM ca raMdhreNa laMbaM pazyeddivAkaram । AtmapradakSiNaM kRtvA zuddhAcamanamAcaret 28 ।
hk transliteration by Sanscript