Which is the best deed and which is the worst deed (other than shirk)?

Question

Can anyone tell me the best deed loved by Allah, the best of best, and the worst which come after shirk?

Answer 1

Best deed.

There's a few differing ahadith. It seems natural to believe that belief in Allah is the best deed:

The Prophet was asked, "Which is the best deed?" He said, "To believe in Allah and His Apostle."
_{Sahih al-Bukhari 1519; see also Sunan an-Nasa'i 4985 and Sunan an-Nasa'i 3129}

Beyond this, it's considered context-dependent, i.e., what's the "best deed" differs from person to person and depends on the setting. IslamWeb describe adhering to obligatory acts the best.

Here's some other responses given by the Prophet:

The best of the deeds or deed is the (observance of) prayer at its proper time and kindness to the parents.
_{Sahih Muslim 85 e; see also Sunan Abi Dawud 426 and Jami` at-Tirmidhi 170}

Take to fasting, for there is nothing equal to it.
_{Sunan an-Nasa'i 2222 [grade: sahih]}

Jihad in the cause of Allah.
_{Sunan an-Nasa'i 2624 [grade: sahih]; see also Sunan an-Nasa'i 3130}

Worst deed (other than shirk).

Scholars have distinguished seven destructive sins:

1. shirk,
2. witchcraft,
3. murder,
4. devouring the property of an orphan,
5. consuming usury,
6. fleeing from the battlefield, and
7. slandering chaste women.

These are listed in fatawa by Islam Q&A and About Islam; see also What are the major sins in Islam?

I'm not aware of which of these is considered worst after shirk. The relevant hadith here is:

There is no one who offers the five (daily) prayers, fasts Ramadan, pays Zakah and avoid the seven major sins, but the gates of Paradise will be opened to him, and it will be said to him: Enter in peace. ...
_{Sunan an-Nasa'i 2438 [grade: hasan]}

So it's possible the worst after shirk might also be one of: failing to pray, failing to fast during Ramadan, or failing to pay zakat.