Allaah (subhaanahu wa ta'aala) said:

"They ask you (O Muhammad sal-Allaahu 'alayhe wa sallam) about the Hour, - when will be its appointed time? You have no knowledge to say anything about it, To your Lord belongs (the knowledge of) the term thereof? You (O Muhammad sal-Allaahu 'alayhe wa sallam) are only a warner for those who fear it, The Day they see it, (it will be) as if they had not tarried (in this world) except an afternoon or a morning." [An-Nazi'aat (79):42-46]

"They ask you about the Hour (Day of Resurrection): 'When will be its appointed time?' Say: 'The knowledge thereof is with my Lord (Alone). None can reveal its time but He. Heavy is its burden through the heavens and the earth. It shall not come upon you except all of a sudden.' They ask you as if you have a good knowledge of it. Say: 'The knowledge thereof is with Allaah (Alone) but most of mankind know not.''" [Al-A'raaf (7):187]

Footnotes

[1] Bukhaaree, Kitaab at-Tafsir, commentary on Surat an-Nazi'aat, 6/206.

[2] A similar Hadeeth was narrated by Bukhaaree in Kitaab al-Adab.

[3] See Bukhaaree, Kitaab al-Adab; Muslim, Kitaab al-Fitan wa Ashraat al-Sa'ah.

[4] Bukhaaree, Kitaab at-Tafsir, commentary on Luqman 31:34. A longer Hadeeth is narrated by Muslim in Kitaab al-Eemaan.

[5] Muslim, Kitaab al-Fitan wa Ashraaat al-Sa'ah; Abu Daawood, Kitaab al-Fitan wa'l-Malahim.

[6] The whole speech is narrated by Imaam Ahmad in his Musnad, 2/61. Checker's Note: Da`eef, al-Musnad (3/61) [or 2/61 as stated in the book??], at-Tirmidhee and al-Hakim (4/505). Da`eef due to `Alee ibn Zayd ibn Jad'an. al-Mishkat: 5145 of al-Albaanee. Parts of the complete speech are authentic, see Ibn Kathir's comments