Allah (سبحانه و تعالى) says:
Arabic: وَاسْتَعِينُواْ بِالصَّبْرِ وَالصَّلَوةِ وَإِنَّهَا لَكَبِيرَةٌ إِلاَّ عَلَى الْخَـشِعِينَ
Translation: And seek help in patience and As-Salat (the prayer) and truly, it is extremely heavy and hard except for Al-Khashi`in.
From the Tafsir of Ibn Kathir:
Allah commanded His servants to use patience and prayer to acquire the good of this life and the Hereafter. Muqatil bin Hayan said that this Ayah means, “Utilize patience and the obligatory prayer in seeking the Hereafter. As for patience (here), they say that it means fasting.” There are similar texts reported from Mujahid. Al-Qurtubi and other scholars commented, “This is why Ramadan is called the month of patience,” as is mentioned in the Hadith literature. It was also said that `patience’ in the Ayah means, refraining from evil, and this is why `patience’ was mentioned along with practicing acts of worship, especially and foremost, the prayer. Also, Ibn Abi Hatim narrated that `Umar bin Al-Khattab said, “There are two types of patience: good patience when the disaster strikes, and a better patience while avoiding the prohibitions of Allah.” Ibn Abi Hatim said that Al-Hasan Al-Basri was reported to have said similarly.
Allah then said,
(And As-Salah (the prayer).)
The prayer is one of the best means of assistance for firmly adhering to Allah’s orders, just as Allah said;
اتْلُ مَا أُوْحِىَ إِلَيْكَ مِنَ الْكِتَـبِ وَأَقِمِ الصَّلَوةَ إِنَّ الصَّلَوةَ تَنْهَى عَنِ الْفَحْشَآءِ وَالْمُنْكَرِ وَلَذِكْرُ اللَّهِ أَكْبَرُ
(Recite (O Muhammad ) what has been revealed to you of the Book (the Qur’an), and perform As-Salah. Verily, As-Salah (the prayer) prevents from Al-Fahsha’ (i.e. great sins of every kind), and Al-Munkar and the remembrance of (praising) of (you by) Allah is greater indeed) (29:45).
The personal pronoun in the Ayah,
(And truly, it is extremely heavy and hard) refers to prayer, as Mujahid is reported to have said, and it was also the choice of Ibn Jarir. It is possible that the pronoun might be referring to the advice – to observe patience and the prayer – mentioned in the same Ayah. Similarly, Allah said about Qarun (Korah),
وَقَالَ الَّذِينَ أُوتُواْ الْعِلْمَ وَيْلَكُمْ ثَوَابُ اللَّهِ خَيْرٌ لِّمَنْ ءَامَنَ وَعَمِلَ صَـلِحاً وَلاَ يُلَقَّاهَآ إِلاَّ الصَّـبِرُونَ
(But those who had been given (religious) knowledge said: “Woe to you! The reward of Allah (in the Hereafter) is better for those who believe and do righteous good deeds, and this, none shall attain except As-Sabirun (the patient).”) (28:80).