I'TIKAF

1. I'TIKAF in the first ten and in the mid ten days of Ramadan:

Abu Sai'id Al-Khudri Radiyallahu Anh narrated that the Messenger of Allah (PBUH) observedI'tikaf in the first ten days of Ramadan; he then observed I'tikaf in the middle ten days in a Turkish tent with a mat hanging at its door. The Prophet (PBUH) took hold of that mat and place it in the nook of the tent. He then put his head out, and talked with people who came nera him, and he said: I observed I'tikaf in the first ten nights and days in order to seek that night (Night of Decree). I then observedI'tikaf in the middle ten days. Then an angel was sent to me, and I was told that this night is among the last ten nights. He who among you like to observe I'tikaf may do so," and people observed it along with him, and he again said: "That Night of Decree was shown to me in an odd night and I saw in the dream that I was prostrating in the morning in mud and water." So in the morning of the twenty-first night when the Prophet (PBUH)got up for dawn prayer, there was rainfall and the mosque dripped, and I saw mud and water. When he came out after he finished the morning prayer, he saw that his forehead and the tip of his nose had traces of mud and water, and that was the twenty-first night of the last ten nights of Ramadan. (Bukhari 2018). (Source: Summarized Sahih Muslim, Volume 1, Hadith 632)

2. I'tikaf in the last ten days of Ramadan
'Aishah Radiyallahu Anha narrated that the Prophet (PBUH) was regular in observing I'tikaf in the last ten (days) of Ramadan until Allah, the Exalted and Glorious, collected him. His wives also used to observe I'tikaf with him. (Bukhari 2026). (Source: Summarized Sahih Muslim, Volume 1, Hadith 633)

2.1. Striving hard in the last ten (of Ramadan)
'Aishah Radiyallahu Anha narrated that when the last ten nights of Ramadan began the Messenger of Allah (PBUH) kept awake at nights (for prayer and worship), awoke his family, strove hard and fastened his lower garment. (Bukhari 2024) (Source: Summarized Sahih Muslim, Volume 1, Hadith 634)

3. Lailat-ul-Qadr (Night of Decree) and seeking it in the last ten (nights) of Ramadan
Ibn 'Umar Radiyallahu Anhuma narrated that the Messenger of Allah (PBUH) said: "Seek it (Lailat-ul-Qadr) in the last ten (nights). If one of you shows slackness in the earlier part of Ramadan, let it not be weak to observe the last seven." (Bukhari 2015) (Source: Summarized Sahih Muslim, Volume 1, Hadith 635)

4. Lailat-ul-Qadr was the twenty-third night of Ramadan
'Abdullah bin Unais Radiyallahu Anh narrated that the Messenger of Allah (PBUH) said: "I was shown Lailat-ul-Qadr; then I was made to forget it. I saw that I was prostrating in water and mud in the morning of that night." The narrator said: There was a downpour on the twenty-third night and the Messenger of Allah (PBUH) led us in prayer, and as he went back, there was a trace of water and mud on his forehead and on his nose. The narrator added: "Abdullah bin Unais used to say that it was the twenty-third night.(Source: Summarized Sahih Muslim, Volume 1, Hadith 636)

5. Seek it (Lailat-ul-Qadr) in the ninth and seventh and the fifth (in the last ten nights of Ramadan):
Abu Sa'id Al-Khudri Radiyallahu Anh narrated: The Messenger of Allah (PBUH) observed I'tikaf in the middle ten days of Ramadan to seek Lailat-ul-Qadr, before it was shown to him. When these nights were over, he ordered a tent to be pitched. Then it was shown to him that (Lailat-ul-Qadr)was in the last ten nights of Ramadan. Then he ordered to pitch the tent again. He then came to people and said: "O people, Lailat-ul-Qadr was shown to me and I came out to tell you about it, but two man were quarrelling with each other, and there was a devil along with them, and I forgot it. So seek it in the last ten nights of Ramadan. Seek it on the ninth, on the seventh and on the fifth." One of the narrators said: "Abu Sa'id, you know more than about numbers." He said: "Yes, indeed we know better than you." I said: "What is this ninth, seventh, and fifth?" He said: "When twenty-one nights are over and the twenty-second begins, it is the ninth; and when twenty-three nights are over, that which follows is the seventh; and when twenty-five nights are over, what follows is the fifth."(Bukhari2016) (Source: Summarized Sahih Muslim, Volume 1, Hadith 637)

courtesy of tunku