(And your Lord has decreed that you worship none but Him, and be good to parents) meaning: and He commanded goodness toward parents, which means: dutifulness. (If one of them or both of them reach old age while in your care, then do not say to them, 'Uff') Al-Hasan's interpretation is: He says, if they reach old age in your care, or one of them does, and you deal with them as they dealt with you in your childhood, and you detect from them an odor that offends you, then do not say to them: 'Uff'.
Muhammad said: It is also said that the meaning is: Do not say anything to them that contains the slightest expression of annoyance. (And do not shout at them) meaning: do not speak harshly to them, (and speak to them a noble word) meaning: soft and gentle.
﴿وَقَضَى رَبُّكَ أَلَّا تَعْبُدُوا إِلا إِيَّاه وبالوالدين إحسانا﴾ أَيْ: وَأَمَرَ بِالْوَالِدَيْنِ إِحْسَانًا؛ يَعْنِي: بِرًّا ﴿إِمَّا يَبْلُغَنَّ عِنْدَكَ الْكِبَرَ أَحَدُهُمَا أَوْ كِلاهُمَا فَلا تَقُلْ لَهما أُفٍّ﴾ تَفْسِيرُ الْحَسَنِ: يَقُولُ: إِنْ بَلَغَا عِنْدَكَ الْكِبَرَ أَوْ أَحَدُهُمَا، فَوَلِيتَ مِنْهُمَا مَا وَلِيَا مِنْكَ فِي صِغَرِكَ فَوَجَدْتَ مِنْهُمَا رِيحًا تُؤْذِيكَ؛ فَلَا تَقُلْ لَهُمَا: أُفٍّ.
قَالَ مُحَمَّدٌ: وَقِيلَ: الْمَعْنَى: لَا تَقُلْ لَهُمَا مَا فِيهِ أَدْنَى تَبَرُّمٍ. ﴿وَلَا تنهرهما﴾ لَا تُغْلِظَ لَهُمَا الْقَوْلَ ﴿وَقُلْ لَهما قولا كَرِيمًا﴾ أَي: لينًا سهلا
