Paraskaragrihyasutra 2.11

If (a strong) wind is blowing, and on the new-moon day there is an entire interruption of study.

If one has partaken of a Srâddha dinner, if a meteor falls, or distant thundering is heard, or if the earth quakes, or if fiery apparitions are seen, and when a new season begins, (the study shall be interrupted) until the same time next day.

If the Utsarga ceremony has been performed, if clouds appear,...., (it shall be interrupted) through a period of three nights or till twilight has thrice passed.

After he has eaten, until he has (washed and) dried his hands; while being in water; at nighttime; at the time of the morning and evening twilight; while a dead body or a Kandâla is in the village.

While running, while seeing a person of bad fame or who has lost his caste, if a miraculous or happy event happens, as long as (that which occasions the interruption of study) endures.

If hoar-frost (lies on the ground), if a musical instrument is heard, or the cry of a person in pain, at the border of the village, in a burial ground, or if a dog, an ass, an owl, a jackal, or a Sâman song is heard, or if a learned person approaches, as long as (that occasion) endures.

If his Guru has died, let him go down into water (for offering water-oblations) and interrupt (the study) for ten nights.

If one who has performed with him the Tânûnaptra ceremony, or a fellow-pupil (has died), for three nights.

If one who is not his fellow-pupil, (has died,) for one night.

After having studied five months and a half, they should celebrate the Utsarga,

Or six months and a half.

They then mutter this Rik: 'Ye two young sages! The relation which has expired among us, the friendship we dissolve, (turning away) from the condition of friendship.'

After having remained together through a period of three nights, they separate.