Al-Kāfi - Volume 7 > A Deceased Leaves behind Just his Wife
Hadith #3

3- حُمَيْدُ بْنُ زِيَادٍ عَنِ الْحَسَنِ بْنِ مُحَمَّدٍ عَنْ وُهَيْبِ بْنِ حَفْصٍ عَنْ أَبِي بَصِيرٍ عَنْ أَبِي جَعْفَرٍ (عَلَيْهِ السَّلام) فِي رَجُلٍ تُوُفِّيَ وَتَرَكَ امْرَأَتَهُ فَقَالَ لِلْمَرْأَةِ الرُّبُعُ وَمَا بَقِيَ فَلِلإمَامِ‏.

3. Humayd ibn Ziyad has narrated from al-Hassan ibn Muhammad from Wuhayb ibn Hafs from abu Basir who has narrated the following: “About the case of a woman who dies and leaves behind her husband, abu Ja‘far, ‘Alayhi al-Salam, has said, ‘One-fourth belongs to the woman and the rest belongs to the Imam.’”