Praise be to Allah.

Firstly: 

The revelation ceased for the Messenger of Allah (blessings and peace of Allah be upon him) on two occasions: once at the beginning of the revelation, after which Soorat al-Muddaththir was revealed, then after a number of soorahs had been revealed, after which period, Soorat ad-Duha was revealed. 

It was narrated from Jaabir ibn ‘Abdullah (may Allah be pleased with him) that he heard the Messenger of Allah (blessings and peace of Allah be upon him) say: “Then the Revelation ceased for a while, then whilst I was walking, I heard a voice from heaven. I raised my head, and there was the angel who had come to me in Hira’, sitting on a throne between heaven and earth. I was stricken with terror and I fell to the ground. Then I came to my family and said, ‘Cover me, cover me!’ Then Allah, may He be exalted, revealed the verses: ‘O you (Muhammad) enveloped in garments! … And keep away from Ar‑Rujz (the idols)!’ [al-Muddaththir 74:1-5].” 

Narrated by al-Bukhaari (3238) and Muslim (161). 

An-Nawawi (may Allah have mercy on him) said: 

The words “then revelations came one after another” mean, after that period during which the revelation had ceased. The correct view is that the first thing to be revealed was “Iqra’” (Read – i.e., Soorat al-‘Alaq), and the first thing to be revealed after the period during which the revelation had ceased was “O you (Muhammad) enveloped in garments! (i.e., Soorat al-Muddaththir)”. End quote. 

Al-Bukhaari (4953) narrated the hadith of ‘Aa’ishah about the beginning of the revelation, in which the Prophet (blessings and peace of Allah be upon him) told Waraqah about what he had seen, and Waraqah said to him: If I live to see that day, I will support you wholeheartedly. ‘Aa’ishah said: But soon after that Waraqah died, and the revelation ceased for a while. 

This was the first period during which the revelation ceased.

Al-Bukhaari (4950) and Muslim (1797) narrated that Jundub ibn Sufyaan (may Allah be pleased with him) said: The Messenger of Allah (blessings and peace of Allah be upon him) fell sick and did not get up to pray qiyaam for two or three nights. Then a woman came and said: O Muhammad, I hope that your shaytaan has left you; I have not seen him approach you for two or three nights. Then Allah, may He be glorified and exalted, revealed the words ((interpretation of the meaning):

“By the forenoon (after sunrise).

2. By the night when it darkens (and stands still).

3. Your Lord (O Muhammad (blessings and peace of Allah be upon him)) has neither forsaken you nor hates you”

[al-Duha 93:1-3]. 

This was the second period during which the revelation ceased.

Al-Haafiz Ibn Hajar (may Allah have mercy on him) said: 

The period (of cessation of the revelation) mentioned as the reason for revelation of Soorat ad-Duha was something other than the period (of cessation of the revelation) that occurred at the beginning of the revelation. The latter lasted for many days, whereas the latter only lasted for one or two nights.

End quote from Fath al-Baari (8/710) 

Ibn ‘Ashoor (may Allah have mercy on him) said: 

The cessation of revelation to the Prophet (blessings and peace of Allah be upon him) happened on two occasions: 

The first one was before the revelation of Soorat al-Muddaththir or al-Muzzammil. That was when the Messenger of Allah (blessings and peace of Allah be upon him) feared that the revelation had ceased (completely), and that is the period after which he saw Jibreel seated on a throne between heaven and earth. 

The second occasion was after approximately eight soorahs had been revealed, i.e., those that were revealed after the first period (of cessation of revelation), so it came after ten soorahs (in total) had been revealed.

End quote from at-Tahreer wa’t-Tanweer (30/396). 

Secondly: 

The scholars differed as to how long the first period of cessation of revelation lasted. It was said that it was three years, or approximately two years, or two and a half years, or twelve days, or fifteen days, or forty days, and so on. 

Al-Haafiz (may Allah have mercy on him) said: 

In the Taareekh of Ahmad ibn Hanbal it was narrated from ash-Shu‘bi that the period of the cessation of revelation lasted for three years. This was stated categorically by Ibn Ishaaq. End quote from Fath al-Baari (1/27) 

Ibn Katheer said: 

Some of them said: the period of cessation of revelation lasted for approximately two years or two and a half years. 

End quote from al-Bidaayah wa’n-Nihaayah (4/42) 

Ar-Raazi (may Allah have mercy on him) said: 

The scholars differed concerning the length of the period during which the Revelation ceased. Ibn Jurayj said: It was twelve days. Al-Kalbi said: It was fifteen days. Ibn ‘Abbaas said: It was twenty-five days. As-Suddi and Muqaatil said: It was  forty days.

End quote from Tafseer ar-Raazi (31/192) 

Ibn ‘Aashoor said:

It was said that the first period during which the Revelation ceased was forty days.

End quote from at-Tahreer wa’t-Tanweer (30/396) 

With regard to the second period during which the Revelation ceased, it was true or three nights, as mentioned above in the hadith of Jundub ibn Sufyaan (may Allah be pleased with him) 

Ibn Katheer (may Allah have mercy on him) said: 

Soorat ad-Duha was revealed after another period (of cessation of revelation), that lasted for a few nights, as is proven in as-Saheehayn and elsewhere.

End quote from al-Bidaayah wa’n- Nihaayah (4/41) 

Thirdly: 

The wisdom behind the temporary cessation of revelation was so that the fear that the Messenger of Allah (blessings and peace of Allah be upon him) had felt when Jibreel (peace be upon him) first came down to him might dissipate, and so that he might long for the return of the revelation, and so that consolation might come down to the Messenger of Allah (blessings and peace of Allah be upon him) from Allah, may He be exalted, thus increasing him in faith and steadfastness. It was also so that Allah might test the people, so that the believers would become steadfast and the disbelievers would go astray. 

Al-Haafiz Ibn Hajar (may Allah have mercy on him) said: 

The cessation of revelation refers to it being delayed for a period of time. This was so that what the Prophet (blessings and peace of Allah be upon him) felt of fear might dissipate, and so that he would long for its return.

End quote from Fath al-Baari (1/27) 

Mu‘tamir ibn Sulaymaan said, narrating from his father: When the revelation ceased for a while, they said: If it was really from Allah, revelations would come one after another, but Allah has forsaken him and hates him. Then Allah revealed “By the forenoon (after sun-rise)” [i.e., Soorat ad-Duha 93] and “Have We not lifted up your heart ” [.e., Soorat al-Inshiraah 94] in full. 

End quote from Fath al-Baari (8/710) 

Fourthly: 

It is not known exactly what the Prophet (blessings and peace of Allah be upon him) did during the period when the revelation ceased, but what is definitely known is that this saddened him and that he longed for it to return and hoped to find comfort in it after what had befallen him of alarm and fear the first time. 

Ibn Ishaaq (may Allah have mercy on him) said: 

Then the revelation stopped for a time, so that the Messenger of Allah (blessings and peace of Allah be upon him) was distressed and saddened. Then Jibreel brought him Soorat ad-Duha, in which his Lord, Who had so honoured him, swore that He had not forgotten him and did not hate him.

End quote from Seerat Ibn Hishaam (1/225)