Abu lQasim (ﷺ) said: When one of you is in the sun (Shams)--Makhlad's version has "fay'"--and the shadow withdraws from him so that he is partly in sun and partly in shade, he should get up.
Reference: Sunan Abi Dawud 4821 In-book : Book 43, Hadith 49 English translation : Book 42, Hadith 4803
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