Are hasanaat and sayi’aat multiplied at special times and in special places?
Question

Is it true that sayi’aat (bad deeds) are multiplied in Ramadan? Is the same true of hasanaat (good deeds)? Is there any evidence to that effect?.
Praise be to Allah.Yes, both hasanaat and sayi’aat are multiplied at special times and in special places, but there is a difference between the multiplication of hasanaat and the multiplication of sayi’aat. The multiplication of hasanaat is in both quantity and quality. What is meant by quantity is number, so a good deed is multiplied by ten times the like thereof; and what is meant by quality is that the reward is great and vast. With regard to sayi’aat, it is multiplied in terms of quality only, i.e., the sin is greater and the punishment is more severe. With regard to quantity a bad deed receives one sayi’ah, and it cannot be more than one. 
It says in Mataalib Uli al-Nuha (2/385): 
“Hasanaat and sayi’aat are multiplied in a special place such as Makkah, Madeenah and Bayt al-Maqdis (Jerusalem), and in the mosques; and at special times such as on Fridays, during the sacred months and in Ramadan. With regard to the multiplication of hasanaat, this is a matter concerning which there is no scholarly difference of opinion. With regard to the multiplication of sayi’aat, this was the view of a number of scholars, following Ibn ‘Abbas and Ibn Mas’ood… Some scholars said that what Ibn ‘Abbas and Ibn Mas’ood meant by the view on the multiplication of sayi’aat is that they are multiplied in quality but not in quantity.”
Shaykh Ibn Baaz (may Allah have mercy on him) said: “Does fasting bring the Muslim expiation for both minor and major sins? Is the sin of an evil action compounded in Ramadan?” 
He replied: “What is prescribed for the Muslim in Ramadan and at other times is to strive against his nafs (self) that is inclined towards evil until it becomes tranquil and inclined towards goodness. He must fight against the enemy of Allah Iblees until he is safe from his evil and his whispers. The Muslim in this world is engaged in a great, ongoing struggle against his nafs, his desires and the Shaytaan. So he has to repent a great deal and pray for forgiveness at all times. But times vary one from another. The month of Ramadan is the best month of the year, for it is the month of forgiveness, mercy and ransom from the Fire. If the month is special and the place is special, the hasanaat for good deeds are multiplied and the sayi’aat for sins are multiplied. An evil deed done in Ramadan is more sinful than one done at any other time, just as an act of worship done in Ramadan brings a greater reward from Allah than one done at any other time. Because Ramadan has such a great status, an act of worship done during this month is especially virtuous and its reward is greatly multiplied, and a sin committed during this month is worse and more serious than a sin committed at any other time. So the Muslim has to make the most of this blessed month by doing acts of worship and righteous deeds, and giving up bad deeds, so that Allah may bless him by accepting his good deeds and helping to remain steadfast in adhering to the truth. But a bad deed receives one sayi’ah like it, and is not multiplied in terms of quantity either in Ramadan or at other times. But a good deed may be multiplied ten or more times, because Allah says in Soorat al-An’aam (interpretation of the meaning): 
“Whoever brings a good deed (Islamic Monotheism and deeds of obedience to Allah and His Messenger) shall have ten times the like thereof to his credit, and whoever brings an evil deed (polytheism, disbelief, hypocrisy, and deeds of disobedience to Allah and His Messenger) shall have only the recompense of the like thereof, and they will not be wronged” [al-An’aam 6:160] 
And there are many similar verses. 
Similarly in special places such as the Haramayn [the Two Sanctuaries, i.e., in Makkah and Madeenah] deeds are multiplied greatly in quantity and quality; bad deeds are not multiplied in quantity but they are multiplied in quality when done at special times or in special places, as referred to above. And Allah is the Source of strength. 
From Majmoo’ Fatawa wa Maqaalaat Mutanawwi’ah, 15/446. 
Shaykh Ibn ‘Uthaymeen said in al-Sharh al-Mumti’, 7/262: 
Both hasanaat and sayi’aat are multiplied when done in special places and at special times.  
Hasanaat (good deeds) are multiplied in quantity and quality; sayi’aat (bad deeds) are multiplied in quality but not in quantity, because Allah says in Soorat al-An’aam, which was revealed in Makkah, (interpretation of the meaning): 
“Whoever brings a good deed (Islamic Monotheism and deeds of obedience to Allah and His Messenger) shall have ten times the like thereof to his credit, and whoever brings an evil deed (polytheism, disbelief, hypocrisy, and deeds of disobedience to Allah and His Messenger) shall have only the recompense of the like thereof, and they will not be wronged”
[al-An’aam 6:160] 
And He says (interpretation of the meaning): 
“… and whoever inclines to evil actions therein [i.e., in al-Masjid al-Haraam in Makkah] or to do wrong (i.e. practise polytheism and leave Islamic Monotheism), him We shall cause to taste from a painful torment”
[al-Hajj 22:25] 
But He did not say, We will multiply that to him, rather He said, “We shall cause to taste from a painful torment”. So the way in which sayi’aat done in Makkah or in Madeenah are multiplied is in terms of quality. 
And Allah knows best.