Sources
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Rebbi Abbahu in the name of Rebbi Eleazar: He who puts on tefillin in the night transgresses a positive commandment. What is the reason? (Ex. 13:10) “ “You shall keep this law in its time, from day to day;” “days” not night, “to days” to exclude Sabbaths and holidays. But Rebbi Abbahu sat studying at night with his tefillin on his head! He put them on the side; they were like a deposit in his keeping. Some want to say, he only meant not to put them on…