الكافي- ط الاسلامية, volume 3, page 277

7. Ali ibn Ibrahim has narrated from his father from Salih ibn Sa‘id from Yunus from certain persons of his people who has said the following: “I once asked abu ‘Abdullah (a.s.), about the meaning of Hadith that says, ’Perform al- Dhuhr Salah (prayer) when the sun is equal to one length or two, one yard or two or one step or two steps from this and from there. When is it and how is it? At certain times is half of one step.’ He (the Imam) said that in the Hadith is it said, ‘ An object’s shadow’ and not the shadow of an object’ is because the shadow of an object may appear in different sizes, sometimes longer and sometimes shorter, but an object is an object all the time and it does not change. Hadith has said that it is one yard or two yards, one step or two steps.” Thus one yard or two yards have become explanation of one length or two lengths during the time when an object’s shadow is of the size of one yard and two object’s shadows of the size of two yards. Therefore one object’s or two objects’ shadows and one yard or two yards are in agreement with each other in times as understood one, explaining the other and supported thereby. At a given time, for example at one O’clock, when an object’s shadow is of the size of one yard the time (for Salah (prayer)) is one yard of an object’s shadow and the object is a yard of the shadow. When an object’s shadow is less or more, the time is measured in yards or two yards. This is the explanation of one length and a yard or two yards.’” (The theme of Hadith is obvious; it only may need a little thinking to grasp it fully.)

Translation: Muhammad Sarwar·Thaqalayn link·The Arabic above is the original.

8. Ali ibn Muhammad has narrated from Sahl ibn Ziyad from Muhammad ibn al-Hassan from ‘Abd Allah ibn ‘Abd al-Rahman from Misma’ ibn ‘Abd Malik who has said the following: “He (the Imam) (a.s.), has said, ‘When you complete al-Dhuhr Salah (prayer), it is time for al- ‘Asr Salah (prayer) except that before it there is Nafl (optional Salah (prayer) and it is up to you to make it lengthy or a short one.’”

Translation: Muhammad Sarwar·Thaqalayn link·The Arabic above is the original.