Brihat Parashara Hora Shastra
दिनत्र्यंशेषु सौम्यार्कशनीनां निट्त्रिभागके । चन्द्रशुक्रकुजानां च बलं पूर्णं सदा गुरोः ॥ १२॥
Tribagh Bal. One Rupa is obtained by Budh in the first 1/3 part of day time, by Sūrya in the second 1/3 part of the day and by Śani in the last 1/3 part of the day. Similarly Candr, Śukr and Mangal get full Bal in the first, second and last 1/3 parts of the night. Guru gets this Bal at all times.
english translation
dinatryaMzeSu saumyArkazanInAM niTtribhAgake । candrazukrakujAnAM ca balaM pUrNaM sadA guroH ॥ 12॥
hk transliteration by Sanscript