The Sufficient (Vol 4) · Hadith 688 (#Ḥadīth #2)
Chapter 79 | Minimum Limits of I‘tikaf
2ـ أَحْمَدُ بْنُ مُحَمَّدٍ عَنِ ابْنِ مَحْبُوبٍ عَنْ أَبِي أَيُّوبَ عَنْ أَبِي بَصِيرٍ عَنْ أَبِي عَبْدِ الله (عَلَيْهِ السَّلاَم) قَالَ لا يَكُونُ الاعْتِكَافُ أَقَلَّ مِنْ ثَلاثَةِ أَيَّامٍ وَمَنِ اعْتَكَفَ صَامَ وَيَنْبَغِي لِلْمُعْتَكِفِ إِذَا اعْتَكَفَ أَنْ يَشْتَرِطَ كَمَا يَشْتَرِطُ الَّذِي يُحْرِمُ.
2. Ahmad ibn Muhammad from has narrated from ibn Mahbub from abu Ayyub from abu Basir who has said the following: “Abu ‘Abd Allah , has said, ‘An Ttikaf for less than three days is not valid. One who is in Ttikaf must also fast and it is proper for one in Ttikaf to set a condition as a person in the state of ’Ihram does.’”
Gradings are classical jarḥ-wa-taʿdīl, name-matched to a rijāl index (not individually re-verified).