When does the last third of the night begin and end? – Shaykh Ibn Baaz
Outset and end of the last third of night 
Q: It is reported in the Hadith that Allah descends every night to the lowest heaven in the last third of the night . When does the last third of the night begin and end?
A: There are Mutawatir Hadiths (a Hadith reported by a significant number of narrators throughout the chain of narration, whose agreement upon a lie is impossible) from the Messenger of Allah (peace be upon him) that prove that Allah descends. The Prophet (peace be upon him) stated, Our Lord descends to the lowest heaven every night when the last third of the night begins when He says, ‘Who calls Me to answer him? Who asks Me to give him? Who asks Me for forgiveness to forgive him? 
Ahl-ul-Sunnah wal-Jama`ah (adherents to the Sunnah and the Muslim mainstream) unanimously agreed that Allah descends in a manner that befits Him and that He is not like His creation at all in any of His Attributes, as He states, Say (O Muhammad صلى الله عليه وسلم): “He is Allâh, (the) One. “Allâh-us-Samad (السيد الذي يصمد إليه في الحاجات) [Allâh the Self-Sufficient Master, Whom all creatures need, (He neither eats nor drinks)]. “He begets not, nor was He begotten. “And there is none co-equal or comparable unto Him.” Surah Al-Ikhlas, 112
He (Glorified and Exalted be He) also says, There is nothing like Him; and He is the All-Hearer, the All-Seer.
According to Ahl-ul-Sunnah wal-Jama`ah, we must accept the Ayahs and Hadiths that speak of the Attributes of Allah as they are without Tahrif (distortion of the meaning), Ta`til (denial of Allah’s Attributes), Takyif (descriptive designation of Allah’s Attributes), or Tamthil (likening Allah’s Attributes to those of His Creation). At the same time, we must believe in them and believe that what is mentioned in these texts is true without likening Allah to His creation or discussing the nature of His Attributes. Rather, their view concerning His Attributes is like their view concerning His Dhat (Essence). Ahl-ul-Sunnah wal-Jama`ah affirm the Essence of Allah without Takyif, or Tamthil, and thus, we must also affirm His Attributes without Takyif or Tamthil.
The descent of Allah occurs in every country in a manner that befits Allah, because the descent of Allah is not like the descent of any of His creation. He is described as descending in the last part of the night in all parts of the world in a manner that befits His Majesty, Exalted be He.No one can know how He descends just as no one can know how His Essence is, except Him.
He states, There is nothing like Him; and He is the All-Hearer, the All-Seer.Surah Al-Shura, 42: 11. Allah (Glorified and Exalted be He) also says: So put not forward similitudes for Allâh (as there is nothing similar to Him, nor He resembles anything). Truly! Allâh knows and you know not.Surah Al-Nahl, 16: 74
The time of the first and last third of the night differs according to the season; if the night is nine hours long, then the time of descent begins at the onset of the seventh hour and continues until dawn. If the night is twelve hours long, then the last third begins at the beginning of the ninth hour until the break of dawn and so on, depending on how long or short the night is in each place. May Allah grant us success.
 This was published in Al-Da`wah magazine, issue no. 1138, on 2/9/1408 A.H.
 Al-Bukhari, Sahih, Book on supplications, no. 6321; Muslim, Sahih, Book on travelers* Salah and Salah shortening, no. 758; Al-Tirmidhy, Sunan, Book on Salah, no. 446; Abu Dawud, Sunan, Book on Salah, no. 1315; Ibn Majah, Sunan, Book on performing Prayer and its Sunan, no. 1366; Ahmad ibn Hanbal, Musnad, vol. 2, p. 433; Malik, Al-Muwatta*, Book on call to Prayer, no. 496; and Al-Darimy, Sunan, Book on Salah, no. 1484.’
 Al-Bukhari, Sahih, Book on Friday, no. 1145; Muslim, Sahih, Book on travelers* Salah and Salah shortening, no. 758; Al-Tirmidhy, Sunan, Book on supplications, no. 3498; Abu Dawud, Sunan, Book on Salah, no. 1315; Ibn Majah, Sunan, Book on performing Prayer and its Sunan, no. 1366; Ahmad ibn Hanbal, Musnad, vol. 2, p. 265; Malik, Al-Muwatta*, Book on call to Prayer, no. 496; and Al-Darimy, Sunan, Book on Salah, no. 1479.