[Al-Bukhari and Muslim]
Commentary:
The entire month of Ramadan is a spring season for virtues, worship and obedience of Allah, but its last ten days are the peak of this season of worship. Therefore, one must strive hard in the last ten days and nights of this month to follow the practice of the Prophet (PBUH), to seek the Pleasure of Allah and to attain the benefits of Lailat-ul-Qadr, which occurs during this period. The Prophet (PBUH) used to make special arrangement for observing I`tikaf, and we must also follow this practice of his.
Riyad-us-Saliheen – Hadith No : 1223